.ESSAYS  , 

BIOGRAPHICAL 

AND 

CHEMICAL 


BY 

SIR  WILLIAM   RAMSAY,  K.C.B. 

COMMANDEUR     DE     LA     LEGION     D'HONNEUR 

COMMENDATORE    DELLA   CORONA   D'lTALIA 

FELLOW   OF  THE   ROYAL   SOCIETY,    ETC. 


NEW    YORK 
E.  P.   BUTTON   ANB   COMPANY 

29    WEST    23RD    STREET 
1909 


C-BAL 


PREFACE 

THESE  Essays  on  Chemical  History  and  Biography,  and  on 
chemical  topics,  have  been  delivered  as  lectures,  or  pub- 
lished as  magazine  articles  at  various  times  in  the  course 
of  the  last  twenty-five  years.  A  little  alteration  has  been 
necessary  to  avoid  undue  repetition,  and  in  some  cases 
footnotes  have  been  added,  to  correct  statements  which 
have  been  rendered  inaccurate  by  the  progress  of  dis- 
covery. 

I  have  to  thank  the  University  of  Glasgow  for  permis- 
sion to  reprint  the  oration  on  Black  ;  the  editor  of  the 
Youth's  Companion  for  permission  to  reprint  the  sketch 
of  Lord  Kelvin, '  What  is  an  Element  ? '  '  On  the  Periodic 
Arrangement  of  the  Elements,'  'Radium  and  its  Pro- 
ducts,' '  What  is  Electricity  ? '  and  '  How  Discoveries  are 
Made ' :  the  editor  of  the  Contempora/^y  Review  for 
permission  to  reprint  the  article  on  *  The  Becquerel  Rays ' : 
and  the  Royal  Society,  which  has  kindly  granted  similar 
permission  to  republish  the  life  of  M.  Berthelot. 

WILLIAM  RAMSAY. 

October  1908. 


195100 


CONTENTS 
I.  HISTORICAL  ESSAYS 


PAGE 


THE   EARLY  DAYS   OF  CHEMISTRY                  ...  1 
THE   GREAT  LONDON   CHEMISTS — 

I.    BOYLE  AND  CAVENDISH      .                                  .  19 

II.    DAVY  AND  GRAHAM              .                                  .  41 

JOSEPH  BLACK:    HIS   LIFE  AND   WORK      .                .  .67 

LORD   KELVIN          ....  89 

PIERRE  EUGENE  MARCELLIN   BERTHELOT                 .  101 

II.  CHEMICAL  ESSAYS 

HOW  DISCOVERIES  ARE  MADE       .                .                .  .115 

THE   BECQUEREL   RAYS       .'  129 

WHAT  IS   AN   ELEMENT?   .                 .                 .                 .  147 
ON   THE  PERIODIC  ARRANGEMENT   OF  THE  ELEMENTS      .         161 

RADIUM   AND   ITS   PRODUCTS            .                 .                 .  179 

WHAT   IS   ELECTRICITY?    ...  193 

THE   AURORA   BOREALIS     ....  205 

THE  FUNCTIONS   OF  A   UNIVERSITY              .  227 


vii 


OF   THE 

UNIVERSITY 

OF 


I.  HISTORICAL  ESSAYS 

THE  EARLY  DAYS  OF  CHEMISTRY 

IN  the  early  days  of  the  world's  history,  the  study  of 
science  was  unknown.  The  state  of  society  was  insecure ; 
nation  was  constantly  invading  nation,  and  men  had 
little  leisure  for  other  pursuits  save  war  and  the  chase. 
Yet  we  find,  among  those  nations  which  were  sufficiently 
powerful  to  resist  the  attacks  of  their  neighbours,  and 
sufficiently  prosperous  to  dispense  with  invasions  of  the 
territory  of  others  in  quest  of  plunder,  some  attempts  to 
inquire  into  the  mysteries  of  nature.  In  some  countries, 
as  in  Egypt,  a  leisured  class  of  persons,  the  priests,  urged 
no  doubt  partly  by  a  desire  for  knowledge,  partly  by  a 
wish  to  impress  the  people  with  a  sense  of  their  superior 
powers,  made  some  progress  in  what  may  be  called 
'natural  philosophy/  understanding  by  that  term 
elementary  physics  and  chemistry.  To  these  they  added 
a  considerable  acquaintance  with  astronomy  and  mathe- 
matics. 

For  practical  purposes  of  life,  too,  certain  of  the  arts, 
notably  metallurgy  and  dyeing,  which  are  based  on 
chemical  principles,  were  cultivated.  But  these  were 
carried  on  by  rule  of  thumb,  and  their  development  was 
slow.  Indeed,  they  were  for  the  most  part  in  the  hands 
of  slaves,  the  freemen  finding  it  more  profitable  to 
engage  in  commerce,  or  in  administration.  The  state  of 
Turkey  or  Morocco,  in  the  present  day,  gives  a  good 


2      ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

idea  of  the  condition  of  life  in  the  centuries  before  the 
Christian  era,  in  so  far  as  pursuit  of  science  is  concerned. 
Even  with  the  example  of  adjoining  nations,  whose 
prosperity  is  in  great  part  due  to  the  attention  they 
have  paid  to  the  cultivation  of  scientific  knowledge,  the 
Turks  and  the  Moors  display  a  total  lack  of  interest. 
Much  less,  then,  could  people  such  as  those  be  expected 
to  show  any  eagerness  in  the  discovery  of  Nature's 
secrets. 

Yet  from  time  to  time  there  have  been  minds  who 
refused  to  accept  the  daily  drudgery  of  life  as  sufficient 
for  their  needs.  Questions  such  as :  Whence  did  this 
world  arise  ?  What  does  it  consist  of  ?  What  will  be  its 
ultimate  fate  ?  perplexed  them,  as  they  perplex  us ;  and 
in  an  endeavour  to  answer  questions  like  these,  scientific 
discovery  was  begun.  Many  nations,  however,  were 
instructed  by  the  priests  of  their  religion  that  it  is 
impious  to  make  such  inquiries ;  and  it  is  not  until  the 
era  of  the  early  Greek  civilisation,  when  the  current 
mythology  had  ceased  to  retain  its  hold  on  abler  minds, 
that  we  find  any  serious  attempt  to  grapple  with  funda- 
mental problems  like  those  stated.  But  even  among  the 
Greeks  we  meet  with  a  disinclination  to  take  trouble 
about  matters  which  were  imagined  to  have  little  if  any 
relation  to  human  affairs;  even  Socrates,  one  of  their 
greatest  thinkers,  taught  that  it  was  foolish  to  abandon 
those  things  which  more  nearly  concern  man  for 
things  external  to  him.  Plato,  who  chronicled  the  sayings 
of  Socrates,  wrote  in  the  seventh  book  of  the  Republic : 
1  We  shall  pursue  astronomy  with  the  help  of  problems, 
just  as  we  pursue  geometry;  but  if  it  is  our  desire  to 
become  acquainted  with  the  true  nature  of  astronomy, 
we  shall  let  the  heavenly  bodies  alone.'  And  he  states 
in  another  place,  that  even  if  we  were  to  ascertain  these 
things,  we  could  neither  alter  the  course  of  the  stars, 


THE  EARLY  DAYS  OF  CHEMISTRY  3 

nor  apply  our  knowledge  so  as  to  benefit  mankind.  And 
in  Timaeus,  Plato  remarks, '  God  only  has  the  knowledge 
and  the  power  which  are  able  to  combine  many  things 
into  one,  and  to  dissolve  the  one  into  the  many.  But 
no  man  either  is,  or  ever  will  be,  able  to  accomplish  either 
the  one  or  the  other  operation.' 

Even  in  the  middle  ages,  the  same  spirit  of  content 
with  insufficient  observation,  and  the  same  disposition 
to  draw  conclusions  from  insufficient  premises,  is  to  be 
noticed.  It  is  difficult  for  us,  in  this  age  when  a  certain 
acquaintance  with  scientific  methods  of  thought,  if  not 
with  scientific  facts,  is  common  to  almost  every  one,  to 
imagine  the  kind  of  reply  to  elementary  questions  which 
satisfied  our  predecessors,  even  those  who  devoted  time 
and,  one  would  hope,  some  powers  of  mind  to  a  con- 
sideration of  the  subject.  Let  us  take  a  few  examples. 

The  answer  which  one  of  the  schoolmen  would  give 
to  the  question :  c  Of  what  are  bodies  composed  ? '  is  thus 
paraphrased  by  Le  Febure,  apothecary  to  His  Majesty 
Charles  the  Second :  *  If  the  substance  is  a  body,  it  must 
possess  quantity ;  and  of  necessity,  it  must  be  divisible ; 
now,  bodies  must  be  composed  either  of  things  divisible, 
or  indivisible,  that  is,  either  of  points,  or  of  parts :  a  body, 
however,  cannot  be  composed  of  points,  for  a  point  is 
indivisible,  possessing  no  quantity,  and,  consequently, 
it  cannot  communicate  quantity  to  a  body,  since  it  does 
not  itself  possess  it.  Hence  it  must  be  concluded  that 
a  body  must  be  composed  of  divisible  parts;  to  this, 
however,  it  may  be  said  that  such  parts  must  either  be 
divisible  or  indivisible;  if  the  former,  then  the  part 
cannot  be  the  smallest  possible,  since  it  may  itself  be 
divided  into  others  still  more  minute ;  and  if  this  smallest 
part  is  indivisible,  the  same  difficulty  confronts  us,  for 
it  will  be  without  quantity,  which,  therefore,  it  cannot 
communicate  to  a  body,  for  it  itself  does  not  possess  it, 


4      ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

seeing  that  divisibility  is  the  essential  property  of 
quantity.'  The  logic  is  unanswerable,  but  we  are  left 
where  we  were. 

Let  us  next  see  what  ideas  were  held  by  Du  Clos, 
physician  to  Louis  xiv.,  on  the  cause  of  the  solidification 
of  liquids.  These  are  his  memorable  words : 

'  The  reason  of  the  concretion  of  liquids  is  obviously 
dryness ;  for  this  quality,  being  the  opposite  of  moistness, 
which  renders  bodies  liquid,  may  well  produce  an  effect 
opposite  to  that  produced  by  the  latter,  to  wit,  the 
concretion  of  liquids.'  Again,  we  have  not  gained  much 
information  by  the  profound  utterance. 

One  more  quotation.  It  is  from  a  work  by  Jean  Rey, 
Doctor  of  Medicine,  published  in  1630,  entitled,  'On  an 
Inquiry  wherefore  Tin  and  Lead  increase  in  Weight  on 
Calcination.'  He  is  arguing  that  'Nature  abhors  a 
vacuum,'  a  favourite  thesis  in  former  days.  '  It  is  quite 
certain  that  in  the  bounds  of  nature,  a  vacuum,  which 
is  nothing,  can  find  no  place.  There  is  no  power  in 
Nature  from  which  nothing  could  have  made  the  universe, 
and  none  which  could  reduce  the  universe  to  nothing : 
that  requires  the  same  virtue.  Now  the  matter  would 
be  otherwise  if  there  could  be  a  vacuum.  For  if  it  could 
be  here,  it  could  also  be  there ;  and  being  here  and  there, 
why  not  elsewhere  ?  and  why  not  everywhere  ?  Thus  the 
universe  could  reach  annihilation  by  its  own  forces ;  but 
to  Him  alone  who  could  make  it  is  due  the  glory  of 
compassing  its  destruction.' 

We  must  remember,  therefore,  in  studying  the  early 
history  of  chemistry,  that  not  only  were  facts,  familiar  to 
many  of  us  now,  wholly  unknown ;  but  we  must  also  bear 
in  mind  that  the  point  of  view  from  which  the  early 
chemists  surveyed  the  phenomena  of  nature  was  entirely 
different  from  that  to  which  we  are  now  accustomed. 
It  is  evident,  from  the  examples  quoted,  which  are  not 


THE  EARLY  DAYS  OF  CHEMISTRY  5 

taken  from  the  writings  of,  those  who  lived  at  a  very 
remote  time  from  the  present  day,  but  only  six  or  seven 
generations  ago,  that  our  great-great-great-grandfathers 
differed  from  ourselves  not  merely  in  lack  of  knowledge, 
but  in  the  way  they  regarded  the  facts  which  they 
observed.  And  it  is  consequently  somewhat  difficult  for 
us  to  adopt  their  point  of  view,  and  to  think  their 
thoughts.  But  we  must  attempt  to  do  so,  if  we  are  to 
realise  the  progress  of  our  science. 

The  progress  of  the  science  of  Chemistry,  indeed,  forms 
one  phase  of  the  progress  of  human  thought.  The  ideas 
which  have  been  held,  however,  run  in  certain  channels. 
They  may  all  be  referred  to  speculations  on  the  nature 
of  matter ;  but  the  speculations  take  different  forms. 
For  it  may  be  inquired :  What  forms  is  matter  capable  of 
assuming  ?  Or,  what  is  the  minute  structure  of  matter  ? 
Or,  what  changes  does  matter  undergo  ?  These  three 
questions  were  for  the  ancients,  as  they  are  still  for  us, 
fundamental;  and  it  will  be  the  aim  of  these  essays  to 
endeavour  to  give  the  reader  some  idea  of  the  history 
of  these  three  lines  of  thought.  We  shall  see  that 
our  present  knowledge  enables  us  in  some  measure 
to  connect  these  three  lines  of  inquiry  by  virtue  of 
certain  hypotheses  ;  but  it  will  be  convenient  to  treat 
of  each  separately,  at  least  up  to  a  certain  stage. 


THE   ELEMENTS 

The  word  'Element/ in  the  old  days,  had  a  meaning 
different  from  that  which  we  now  ascribe  to  it ;  or,  to  be 
more  exact,  it  had  two  meanings,  which  were  frequently 
confounded  with  one  another.  The  suggested  derivation 
of  the  word  indicates  one  of  these  meanings ;  it  is  that 
which  we  usually  give  it ;  for,  just  as  '  1,'  ' m,'  and  '  n '  are 


6      ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

constituents  of  the  alphabet,  so  an  '  element '  was  regarded 
as  a  constituent  of  substances.  From  the  use  of  the 
word  by  ancient  authors,  however,  it  would  appear  that 
an  element  was  often  regarded  as  a  property  of  matter ; 
and  it  was  evidently  supposed  that  by  changing  the 
properties,  or  in  the  words  of  the  old  writers  adding  more 
or  less  of  one  or  other  element  to  a  substance,  the 
substance  itself  could  be  transmuted  into  another  wholly 
different.  We  shall  see  examples  of  the  two  meanings 
illustrated  later  on. 

It  is  probable  that  the  original  ideas  of  elements 
reached  Greece  from  India.  The  Buddhistic  teaching 
was  that  the  elements  are  six  in  number,  namely,  Earth, 
Water,  Air,  Fire,  Ether,  and  Consciousness.  But  they  are 
given  by  Empedocles  of  Agrigent,  who  lived  about  440 
B.C.,  without,  the  two  last;  and  many  disputes  arose  as 
to  which  was  to  be  regarded  as  the  primary  one,  from 
which  all  the  others  were  derived ;  for  even  at  that 
remote  date,  speculation  was  rife  as  to  the  unity  of 
matter.  While  Thales  contended  that  the  original 
element  was  water,  Anaximenes  believed  it  to  be  air  or 
fire;  and  Aristotle  did  not  regard  elements  as  different 
kinds  of  matter,  but  as  different  properties  appertaining 
to  one  original  matter.  Plato,  however,  evidently  con- 
sidered elements  to  be  different  kinds  of  matter,  for  he 
puts  these  words  into  the  mouth  of  Timaeus :  'In  the 
first  place,  that  which  we  are  now  calling  water,  when 
congealed,  becomes  stone  and  earth,  as  our  sight  seems 
to  show  us  [here  he  refers  probably  to  rock-crystal,  then 
supposed  to  be  petrified  ice] ;  and  this  same  element, 
when  melted  and  dispersed,  passes  into  vapour  and  fire. 
Air,  again,  when  burnt  up,  becomes  fire,  and  again  fire, 
when  condensed  and  extinguished,  passes  once  more 
into  the  form  of  air ;  and  once  more  air,  when  collected 
and  condensed,  produces  cloud  and  vapour;  and  from 


THE  EARLY  DAYS  OF  CHEMISTRY     7 

these,  when  still  more  compressed,  comes  flowing  water ; 
and  from  water  come  earth  and  stones  once  more;  and 
thus  generation  seems  to  be  transmitted  from  one  to  the 
other  in  a  circle.' 

Aristotle  attributed  to  these  elements  four  properties,  of 
which  each  possessed  two.  Thus,  Earth  was  cold  and 
dry ;  Water,  cold  and  moist ;  Air,  hot  and  moist ;  and 
Fire,  hot  and  dry.  A  fifth  element  was  also  conceived  by 
Aristotle  to  accompany  these  four;  he  termed  it  V\TJ, 
translated  into  the  Latin  Quinta  Essentia ;  and  this  was 
regarded  by  alchemists  of  a  later  date  as  of  the  utmost 
importance,  for  it  was  supposed  to  penetrate  the  whole 
world.  The  ceaseless  strivings  of  the  alchemists  after 
the  'quintessence'  were  due  to  the  notion  that,  were  it 
discovered,  all  transmutations  would  then  be  possible. 
Yet  the  word '  Chemistry'  was  not,  so  far  as  we  know,  in  use 
in  Aristotle's  time.  It  is  said  to  occur  in  a  Greek  manu- 
script of  Zosimus,  a  resident  in  Panapolis,  a  city  in  Egypt, 
who  wrote  in  the  fifth  century.  It  appeared  to  mean  the 
art  of  making  gold  and  silver ;  for  the  title  of  his  work  is 
given  by  Scaliger  as  *  A  faithful  Description  of  the  sacred 
and  divine  Art  of  making  gold  and  silver.'  M.  Berthelot, 
who  has  made  a  detailed  study  of  ancient  Greek,  Arabic, 
Syriac,  and  Latin  manuscripts  relating  to  early  chemistry, 
believes  that  the  attempts  to  transmute  metals  arose,  not 
from  any  philosophical  notions  regarding  the  nature  of 
elements,  but  from  fraudulent  attempts  of  goldsmiths  to 
pass  off  base  metals  on  their  customers  for  silver  and 
gold.  One  of  the  earliest  manuscripts  on  record  dates 
from  the  third  century,  and  is  preserved  at  Leiden  in 
Holland.  It  was  found  in  a  tomb  in  Thebes  in  1828. 
It  is  a  rough  and  ill-spelt  collection  of  workman's  receipts 
for  working  in  metals,  in  which  frequent  reference  is 
made  to  an  alloy  of  copper  and  tin — an  alloy  which  in 
many  respects  resembles  gold.  It  is  apparently  a  manu- 


8      ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

script  which  escaped  the  fate  of  most  of  the  Egyptian  MSS. 
of  that  date;  for  about  the  year  290,  the  Emperor 
Diocletian  commanded  that  all  works  on  alchemy  should 
be  burnt,  *  in  order  that  the  Egyptians  might  not  become 
rich  by  the  art  [of  making  gold  and  silver]  and  use  their 
wealth  to  revolt  against  the  Romans.' 

But  although  the  idea  of  transmutation  did  not  arise 
from  such  theoretical  speculations  as  Aristotle's  on  the 
unity  of  matter,  and  on  the  possibility  of  converting  one 
kind  of  matter  into  another  by  altering  its  properties, 
or  in  the  language  of  the  time,  adding  or  removing  more 
or  less  of  one  or  other  element,  yet  the  later  workers  did 
not  scruple  to  use  Aristotle's  theory  in  order  to  make 
good  their  case.  And  for  many  centuries — indeed  until 
our  own  time — there  have  always  existed  men  who 
devoted  their  lives  to  this  object. 

There  was,  at  the  same  time,  a  supposed  mystical 
connection,  of  Chaldean  origin,  between  the  metals  and 
the  planets.  Thus  gold  was  the  sun ;  silver,  the  moon ; 
copper,  Venus ;  tin,  and  afterwards  mercury,  was  associ- 
ated with  the  planet  of  that  name ;  iron,  used  in  battle, 
had  affinity  with  ruddy  Mars ;  electron,  an  alloy  of  gold 
and  silver,  and  subsequently  tin,  was  Jupiter ;  and  sluggish 
and  heavy  lead  was  the  slow-moving  Saturn.  These 
analogies  were  used  in  casting  horoscopes,  or  predicting 
the  future  of  those  rich  and  credulous  enough  to  consult 
astrologers. 

At  the  same  time  as  these  fantastic  notions  were  held, 
many  processes  of  manufacture,  involving  a  knowledge 
of  chemical  reactions,  were  carried  on.  These  will  be 
alluded  to  later ;  but  it  may  be  noted  here  that  speculation 
did  not  take  the  course  of  attempting  to  devise  explana- 
tions of  chemical  changes,  but  was  indulged  in,  as 
before  remarked,  with  little  reference  to  experimental 
methods. 


THE  EARLY  DAYS  OF  CHEMISTRY  9 

The  conquest  of  Egypt  by  the  Arabians  in  the  seventh 
century  put  an  end  for  a  time  to  the  school  of  learning 
of  Alexandria,  where  citizens  of  all  nations  met  and  dis- 
cussed problems  of  all  kinds.  But  the  spirit  of  the  Grseco- 
Egyptians  was  too  strong  even  for  the  fanaticism  of  the 
Arabians ;  the  conquered  became  the  conqueror ;  and  an 
Arabian  school  of  philosophy  arose,  which  carried  on  the 
traditions  acquired  from  the  Greeks.  It  has  been  be- 
lieved, until  M.  Berthelot  showed  the  belief  to  be  erro- 
neous, that  Latin  works  which  professed  to  be  translations 
from  the  Arabic  of  the  eighth  and  succeeding  centuries 
were  really  renderings  of  the  ancient  Arabian  authors. 
It  appears,  however,  that  they  are  for  the  most  part 
forgeries,  having  little  if  any  resemblance  to  the  originals. 
Thus  Geber,  said  to  have  been  translated  into  Latin  in 
1529,  is  entirely  different  from  the  Arabic  writings  of  the 
real  Geber.  The  historical  Geber  lived  in  the  ninth  cen- 
tury. His  comment  on  alchemy  is  characterised  by 
strong  common  sense.  It  is :  'I  saw  that  persons  em- 
ployed in  attempts  to  fabricate  gold  and  silver  were 
working  in  ignorance,  and  by  false  methods ;  I  then  per- 
ceived that  they  belonged  to  two  classes,  the  dupers  and 
the  duped.  I  pitied  both  of  them.' 

About  this  time,  however,  an  addition  to  Aristotle's 
classification  of  elements  was  made ;  and  it  endured  until 
within  the  last  two  hundred  years.  It  evidently  arose 
from  attempts  to  account  for  the  properties  of  the  metals, 
and  the  changes  which  they  undergo  by  heat.  These 
additional  'principles,'  as  they  were  termed,  were  salt, 
sulphur,  and  mercury.  We  read  that  the  noble  metals 
contain  'a  very  pure  mercury/  the  meaning  being,  pro- 
bably, that  they  possess  a  high  metallic  lustre ;  while  the 
common  metals,  such  as  copper  and  iron,  contain  '  a  base 
sulphur,'  implying  that  these  metals  are  easily  altered  by 
fire,  losing  their  metallic  appearance  and  changing  into 


10    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

black  scales.  These  principles  were  later  increased  to 
five,  by  the  addition  of  '  phlegm '  and  of  '  earth.'  Fanci- 
ful analogies  were  drawn  between  the  Divine  Trinity  of 
Father,  Son,  and  Holy  Spirit,  the  human  Body,  Soul, 
and  Spirit,  and  the  three  principles  above-named.  At- 
tempts were  incessantly  made  to  draw  inspiration  from 
such  impossible  fancies.  Thus  the  volatilisation  of  mer- 
cury, or  '  Spirit '  as  it  was  sometimes  called,  was  deemed 
analogous  to  the  ascension  of  Christ!  In  fact,  there  is 
no  limit  to  the  absurdity  and  folly  of  the  endeavours  of 
the  alchemists.  Let  us  hear  a  list  of  their  processes,  as 
told  by  Sir  George  Ripley,  who  lived  and  wrote  in  1471. 

c  The  fyrst  Chapter  shalbe  of  naturall  Calcination ; 
The  second  of  Dyssolution  secret  and  phylosophycall ; 
The  third  of  our  Elemental  Separation ; 
The  fourth  of  Conjunction  matrymonyall ; 
The  fifth  of  Putrefaction  then  folio  we  shall ; 
Of  Congelatyon,  albyfycative  shall  be  the  Syxt, 
Then  of  Cybation  the  seaventh  shall  follow  next. 
The  secret  of  our  Sublymation  the  eyght  shall  show ; 
The  nynth  shall  be  of  Fermentation ; 
The  tenth  of  our  Exaltation  I  trow ; 
The  eleventh  of  our  mervelose  Multyplycatyon  ; 
The  twelfth  of  Projectyon,  then  Recapytulatyon ; 
And  so  thys  treatise  shall  take  an  end, 
By  the  help  of  God,  as  I  entend.' 

These  chapters  are  wearisome  and  rambling ;  and  it  is 
impossible  to  gain  a  single  clear  idea  from  their  perusal. 
Indeed  it  was  part  of  the  creed  of  the  alchemists  that 
their  secrets  were  too  precious  to  be  revealed  to  the  baser 
sort  of  men. 

1  The  Philosophers  were  y-sworne  eche  one 
That  they  shulde  discover  it  unto  none, 
He  in  no  boke  it  write  in  no  manere 
For  unto  Christ  it  is  so  lefe  and  deare : 


THE  EARLY  DAYS  OF  CHEMISTRY          11 

That  he  wol  not  that  it  discovered  be, 
But  where  it  liketh  to  his  deite : 
Man  to  inspire  and  eke  for  to  defend 
Whan  that  him  liketh  :  in  this  is  his  end ' — 


sang  Chaucer,  and  he  told  a  true  tale,  for  the  meanings  of 
alchemical  expressions  are  often  undecipherable. 

The  green  lion,  the  basilisk,  the  cockatrice,  the  sala- 
mander, the  flying  eagle,  the  toad,  the  dragon's  tail  and 
blood,  the  spotted  panther,  the  crow's  bill,  blue  as  lead, 
kings  and  queens,  red  bridegrooms  and  lily  brides,  and 
many  more  mystical  terms  which  had  no  doubt  some 
meaning  to  adepts,  were  mingled  in  inextricable  con- 
fusion. 

Moreover,  the  alchemists  made  use,  not  only  of  fantastic 
expressions,  in  order  to  preserve  their  supposed  secrets 
from  the  common  people,  but  they  had  also  a  set  of 
symbols,  possibly  originating  from  the  Chaldean  or  Egyp- 
tian alphabets,  by  which  the  substances  and  many  of  the 
processes  used  were  symbolised.  While  the  chief  aim  of 
modern  science  is  perspicuity,  that  of  the  alchemists  was 
ambiguity  and  mystery.  In  many  cases  they  were  so 
successful  in  preserving  their  secrets  that  even  modern 
investigation  has  failed  to  reveal  them.  But  there  is  one 
grain  of  comfort,  albeit  it  savours  of  sour  grapes,  it  is 
perfectly  certain  that  there  was  nothing  worth  revealing ; 
at  least  nothing  which  it  could  profit  a  modern  student 
of  science  to  know.  Where  the  descriptions  have  been 
interpreted,  they  refer  to  imperfect  methods  of  doing 
what  we  are  now  able  to  do  with  much  greater  economy 
and  rapidity.  As  already  pointed  out,  their  theory  of 
elements  was  erroneous ;  they  were,  moreover,  acquainted 
with  very  few  pure  substances,  and  had  no  criterion  of 
the  purity  of  those  they  possessed  ;  and  they  failed  to 
realise  the  existence  of  gases  as  forms  of  matter. 


12    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Yet  the  interminable  experiments  which  were  con- 
ducted with  a  view  of  discovering  the  '  Philosopher's 
Stone/  which  should  convert  the  baser  metals  into  gold, 
and  the  elixir  vitce,  which  should  convey  undying  youth 
on  its  happy  possessor,  led  to  the  discovery  of  many 
chemical  compounds.  The  writings  of  Basil  Valentine, 
reputed  to  have  been  a  Benedictine  monk  living  in  South 
Germany  during  the  latter  half  of  the  fifteenth  century, 
contain  a  description  of  many  substances,  now  known 
as  chemical  entities,  together  with  the  methods  of  pre- 
paring them.  In  a  tract  entitled  '  The  Great  Stone  of  the 
Ancients/  he  gives  in  detail  the  properties  of  ordinary 
sulphur;  of  mercury,  alluding  to  the  medicinal  uses  of 
its  compounds ;  of  antimony  oxide  or  '  Spiessglas/  which 
he  conjectures  to  consist  of  'much  mercury,  also  much 
sulphur,  though  little  salt ' ;  of  copper- water,  or  a  solution 
of  copper  sulphate ;  of  lima  potabilis  or  solution  of  silver 
nitrate;  of  quick-lime;  of  arsenious  oxide;  of  saltpetre. 
The  last  he  makes  tell  its  own  story :  '  Two  elements  are 
found  in  me,  in  quantity — fire  and  air ;  I  contain  water  and 
earth  in  less  amount ;  therefore  am  I  fiery,  burning,  and 
volatile.  For  a  subtle  spirit  resides  in  me ;  I  am  likest  to 
mercury — inwardly  hot  but  outwardly  cold.  My  chief 
enemy  is  common  sulphur;  and  yet  he  is  my  greatest 
friend,  for  I  am  purified  and  refined  through  him.'  Sal- 
ammoniac,  tartar,  vinegar,  and  above  all,  numerous  com- 
pounds of  antimony  were  also  described  by  Basil  Valen- 
tine, the  last  in  his  celebrated  work  entitled,  The  Trium- 
phal Chariot  of  Antimony.  In  his  writings,  however, 
he  points  out  that  many  of  the  substances  he  describes 
have  medicinal  properties ;  and  his  successors,  of  whom 
perhaps  the  best  known  was  Paracelsus,  developed  this 
part  of  his  teaching.  Yet  in  spite  of  his  considerable 
knowledge,  he  retained  belief  in  transmutation :  he  also 
added  one  to  the  previously  received  two  principles  of 


THE  EARLY  DAYS  OF  CHEMISTRY          13 

Geber  and  his  disciples,  namely  salt,  or,  as  he  terms  it, 
'  salt  of  the  philosophers ' ;  it  is  the  constituent  of  matter, 
which  confers  solidity,  and  which  remains  after  the  volatile 
mercury  and  sulphur  have  been  removed  by  heat. 

In  the  first  half  of  the  sixteenth  century  Paracelsus 
extended  and  applied  the  suggestion  of  Basil  Valentine, 
and  founded  what  became  known  as  the  school  of  '  iatro- 
chemists' — a  body  of  men  who  taught  that  the  chief 
object  of  chemistry  is  not  the  transmutation  of  metals, 
but  the  application  of  chemical  substances  to  medical 
uses.  He  adhered,  however,  to  Valentine's  theory  of  the 
three  principles ;  but  he  applied  them  to  the  human 
body,  teaching  that  the  organism  itself  consists  of  these 
principles,  and  that  disease,  owing  its  origin  to  a  deficiency 
of  one  of  them,  is  to  be  combated  by  its  being  restored 
to  the  system.  Increase  of  sulphur,  he  taught,  gives  rise 
to  fever  and  the  plague ;  increase  of  mercury  to  paralysis 
and  depression ;  and  of  salt,  to  diarrhoea  and  dropsy.  Too 
little  sulphur  in  the  organism  produces  gout ;  delirium  is 
caused  by  distilling  it  from  one  organ  to  another,  and  so 
on  in  fanciful  theorisings.  One  of  the  most  fantastic  is  his 
attributing  the  nutrition  of  the  body  to  a  beneficent  spirit, 
named  the  '  Archseus,'  who  resided  in  the  stomach,  and 
presided  over  the  function  of  digestion.  But  these 
curious  notions  have  little  bearing  on  the  development 
of  chemistry.  The  teaching  of  Paracelsus,  however,  had 
the  good  effect  of  directing  attention  to  an  important 
branch  of  chemistry — its  use  in  pharmacy.  And  from 
his  time  onwards,  indeed,  up  to  the  middle  of  last  cen- 
tury, many  of  the  best-known  chemists  had  received  a 
medical  training,  and  the  ranks  of  chemical  investigators 
were  largely  recruited  from  the  medical  profession. 

Although  the  alchemists,  after  the  beginning  of  the 
seventeenth  century,  exercised  little  influence  on  the 
progress  of  chemistry,  they  continued  their  fruitless 


14    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

quest.  The  possibility  of  transmutation  has  always  been 
associated  with  speculations  concerning  the  unity  of 
matter.  And  although  there  is  little  evidence  as  yet  to 
justify  the  supposition  that  all  substances  are  ultimately 
composed  of  matter  of  one  kind,  still  the  history  of  our 
science  contains  many  accounts  of  attempts  to  effect 
transmutation.  One  such  attempt,  in  modern  times,  was 
made  by  Dr.  Samuel  Brown,  who  claimed  to  have  obtained 
silicon  from  paracyanogen,  a  compound  consisting  of  car- 
bon and  nitrogen  alone;  but  subsequent  workers  failed 
to  substantiate  his  results.  There  is,  however,  no  ques- 
tion as  regards  the  honesty  of  Dr.  Brown's  work;  the 
only  conclusion  is  that  he  must  have  omitted  to  take 
sufficient  precautions  against  contamination  of  his  carbon 
compounds  with  silicon.  There  exist  at  present  in  France 
also  secret  societies,  with  such  titles  as  'L'Ordre  de  la 
Rose-Croix,'  and  '  L' Association  alchimique  de  France,' 
the  latter  the  successor  of  one  named  'La  Societe  Her- 
metique.'  One  of  the  latest  of  their  'researches'  was 
carried  out  by  '  Maitre '  Theodore  Tiffereau ;  he  professed 
in  1896  to  have  obtained  compounds  of  carbon — ether 
and  acetic  acid — from  the  metal  aluminium,  sealed  up 
with  nitric  acid  in  a  glass  tube,  and  exposed  to  the  sun's 
rays  for  two  months.  But  the  attempt  to  transmute 
baser  materials  into  gold  still  holds  the  field.  August 
Strindberg  claims  to  have  produced  '  incomplete '  gold 
from  ferrous  ammonium  sulphate ;  and  still  more  recently 
Emmens,  who,  however,  disclaims  the  name  of  alchemist, 
states  that  he  has  converted  Mexican  silver  dollars  into 
gold,  or  more  correctly,  increased  the  small  amount  of 
gold  actually  present  in  such  coins,  by  hammering  the 
metal  exposed  to  an  extremely  low  temperature.  There 
is  reason  to  suspect  the  existence  of  an  element  which 
should  resemble  both  gold  and  silver ;  Emmens  pro- 
fesses to  have  made  this  element,  which  he  names 


THE  EARLY  DAYS  OF  CHEMISTRY          15 

argentaurum,  by  hammering  silver,  and  to  have  trans- 
muted it,  by  a  further  process,  into  gold.  He  claims, 
too,  that  Sir  William  Crookes  has  obtained  proof,  slight 
it  is  true,  though  decisive,  of  an  increase  in  the  quantity 
of  gold  in  a  Mexican  dollar,  after  treating  the  latter  by 
his  process. 

We  have  seen  from  what  precedes  that  the  doctrine 
concerning  elements,  held  from  remote  times,  was  that 
they  were  four  in  number,  earth,  water,  air,  and  fire. 
That  besides  these,  there  exist  three  chemical  or  '  hypo- 
static  '  principles,  to  wit,  sulphur,  mercury,  and  salt.  In 
spite  of  the  refutation  of  such  views  by  the  Honourable 
Robert  Boyle,  which  we  shall  consider  later,  they  lingered 
on  until  the  middle  of  last  century,  being  quoted  in 
almost  all  treatises  on  chemistry.  Macquer's  Chemistry, 
a  text-book  which  obtained  a  wide  circulation  in  its  day, 
gives  the  following  description  of  the  ancient  elements 
(1768):  'Air  is  the  fluid  which  we  constantly  breathe, 
and  which  surrounds  the  whole  surface  of  the  terrestrial 
globe.  Being  heavy,  like  all  other  bodies,  it  penetrates 
into  all  places  that  are  not  either  absolutely  inaccessible 
or  filled  with  some  other  body  heavier  than  itself.  Its 
principal  property  is  to  be  susceptible  of  condensation 
and  rarefaction;  so  that  the  very  same  quantity  of  Air 
may  occupy  a  much  greater  or  a  much  smaller  space, 
according  to  the  different  state  it  is  in.  Heat  and  cold,  or, 
if  you  will,  the  presence  or  absence  of  the  particles  of  Fire, 
are  the  most  usual  causes,  and  indeed,  the  measure  of  its 
condensation  and  rarefaction :  for,  if  a  certain  quantity  of 
air  be  heated,  its  bulk  increases  proportionately  to  the 
degree  of  heat  applied  to  it ;  the  consequence  of  which  is, 
that  the  same  space  now  contains  fewer  particles  than 
it  did  before.'  '  Air  enters  into  the  composition  of  many 
substances,  especially  vegetable  and  animal  bodies ;  fully 
analysing  most  of  them,  such  a  considerable  quantity 


16    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

thereof  is  extricated,  that  some  naturalists  have  suspected 
it  to  be  altogether  destitute  of  elasticity,  when  thus 
combined  with  other  principles  in  the  composition  of 
bodies.' 

After  describing  some  of  the  physical  properties  of 
water,  Macquer  continues :  '  Water  enters  into  the  texture 
of  many  bodies,  both  compounds  and  secondary  principles ; 
but,  like  air,  it  seems  to  be  excluded  from  the  composi- 
tion of  all  metals  and  most  minerals.  For  although  an 
immense  quantity  of  water  exists  in  the  bowels  of  the 
earth,  moistening  all  its  contents,  it  cannot  be  thence 
inferred  that  it  is  one  of  the  principles  of  minerals.  It 
is  only  interposed  between  their  parts ;  for  they  may  be 
entirely  divested  of  it,  without  any  sign  of  decomposition : 
indeed,  it  is  not  capable  of  an  intimate  connection  with 
them.' 

Of  earth  he  says :  '  We  observed  that  the  two  principles 
above  treated  of  are  volatile ;  that  is,  the  action  of  fire 
separates  them  from  the  bodies  they  help  to  compose, 
carrying  them  quite  off  and  dissipating  them.  That  of 
which  we  are  now  to  speak,  namely  earth,  is  fixed,  and 
when  it  is  absolutely  pure,  resists  the  utmost  force  of  fire. 
So  that,  whatever  remains  of  a  body,  after  it  has  been 
exposed  to  the  power  of  the  fiercest  fire,  must  be  con- 
sidered as  containing  nearly  all  earthy  principle,  and 
consisting  chiefly  thereof.'  '  Earth,  therefore,  properly  so 
called,  is  a  fixed  principle  which  is  permanent  in  the  fire.' 
He  then  goes  on  to  distinguish  between  fusible  or  vitrifi- 
able  earths,  and  infusible  or  unvitrifiable  earths,  the  latter 
of  which  are  also  called  absorbent  earths,  from  their  pro- 
perty of  imbibing  water. 

Maquer's  views  regarding  fire  are  as  follows :  '  The  matter 
of  the  sun,  or  of  light,  the  Phlogiston,  fire,  the  sulphureous 
principle,  the  inflammable  matter,  are  all  of  them  names 
by  which  the  element  of  fire  is  usually  denoted.  But  it 


THE  EARLY  DAYS  OF  CHEMISTRY          17 

should  seem  that  an  accurate  distinction  has  not  been 
made  between  the  different  states  in  which  it  exists ;  that 
is,  between  the  phenomena  of  fire  actually  existing  as  a 
principle  in  the  composition  of  bodies,  and  those  which 
it  exhibits  when  existing  separately,  and  in  its  natural 
state :  nor  have  proper  distinct  appellations  been  assigned 
to  it  in  these  different  circumstances.  In  the  latter  state, 
we  may  properly  give  it  the  names  of  fire,  matter  of  the 
sun,  of  light,  and  of  heat ;  and  may  consider  it  as  a  sub- 
stance composed  of  infinitely  small  particles,  continually 
agitated  by  a  most  rapid  motion,  and  of  consequence  essen- 
tially fluid.'  '  The  greatest  change  produced  on  bodies, 
by  its  presence  or  its  absence,  is  the  rendering  them 
fluid  or  solid;  so  that  all  other  bodies  may  be  deemed 
essentially  solid;  fire  alone  essentially  fluid,  and  the 
principle  of  fluidity  in  others.  This  being  presupposed, 
air  itself  might  become  solid,  if  it  could  be  entirely  de- 
prived of  the  fire  it  contains ;  as  bodies  of  most  difficult 
fusion  become  fluid,  when  penetrated  by  a  sufficient 
quantity  of  the  particles  of  fire.' 

An  attempt  has  been  made  in  the  preceding  pages  to 
show  the  manner  in  which  the  world  around  us  was 
regarded.  People  were  content  to  take  as  true  what  they 
were  told ;  in  fact,  it  was  regarded  as  unfitting  that  the 
'  mysteries '  with  which  we  are  surrounded  should  be  too 
minutely  inquired  into.  Great  reverence  was  paid  to 
tradition;  and  more  attention  to  the  celebrity  and  per- 
sonal character  of  those  who  advocated  certain  dogmas 
than  to  the  evidence  in  favour  of  their  intrinsic  probability. 

This  spirit  is  by  no  means  extinct;  the  vast  majority 
of  the  human  race  are  content  to  gain  knowledge  at 
second  hand.  Whether  such  knowledge  is  worth  having 
may  well  be  questioned;  it  is  of  course  impossible  that 
every  man  should  investigate  natural  phenomena  for 
himself ;  but  it  is  at  least  possible  to  place  every  child  in 

B 


18    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

the  position  of  knowing,  in  however  elementary  a  way, 
how  useful  deductions  have  been  drawn  from  observa- 
tion and  experiment,  and  of  emancipating  himself,  to 
some  extent  at  least,  from  the  thraldom  of  intellectual 
authority. 


THE  GREAT  LONDON  CHEMISTS 

I.   BOYLE   AND   CAVENDISH 

THE  country  which  is  in  advance  of  the  rest  of  the  world 
in  Chemistry  will  also  be  foremost  in  wealth  and  in 
general  prosperity.  For  the  study  of  Chemistry  is  so 
closely  bound  up  with  our  development  in  all  kinds  of 
industry,  with  the  arrestment  of  disease,  and  with  our 
success  in  war,  that  it  is  essential  to  a  wealthy,  healthy, 
and  peaceful  nation.  The  electrician  is  dependent  on 
the  chemist  for  the  iron  suitable  for  his  dynamos;  the 
engineer,  for  the  materials  which  he  uses  in  his  con- 
struction ;  and  the  scouring,  bleaching,  and  dyeing  of  the 
fabrics  with  which  we  are  clothed,  the  manufacture  of 
the  paper  on  which  we  write,  and  the  ink  with  which  we 
soil  the  paper ;  the  provision  of  our  food-supply,  and 
the  removal  of  effete  matter  from  our  houses;  the 
preparation  of  our  medicines;  and  the  synthesis  of  the 
high  explosives  with  which  warfare  is  now  conducted ; 
all  these  belong  to  the  domain  of  the  chemist,  and 
without  them  we  should  lapse  into  the.  semi-barbarism 
of  our  ancestors. 

Still,  it  must  be  borne  in  mind  that  we  are  far  from 
perfection.  No  process  is  so  perfect  that  there  is  not 
plenty  of  room  for  improvement.  There  is  no  finality 
in  science.  And  that  which  to-day  is  a  scientific  toy 
may  be  to-morrow  the  essential  part  of  an  important 
industry.  This  is  one,  though  not  in  my  view  the  most 
important,  inducement  to  study  the  science  of  Chemistry. 

19 


20    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

To  extend  the  bounds  of  human  knowledge,  and  in  so 
doing  to  glorify  our  Creator,  is  surely  still  more  an  end 
to  be  striven  after.  To  quote  from  the  words  of  Francis 
Bacon,  prefixed  by  Charles  Darwin  to  his  Origin  of 
Species:  'To  conclude,  therefore,  let  no  man,  out  of  a 
weak  conceit  of  sobriety  or  an  ill-applied  moderation, 
think  or  maintain  that  a  man  can  search  too  far,  or  be 
too  well  studied  in  the  book  of  God's  -words,  or  in  the 
book  of  God's  works,  divinity,  or  philosophy ;  but  rather 
let  men  endeavour  an  endless  progress  or  proficience  in 
both.'  Yet  the  acquisition  of  wealth  and  fame  will  pro- 
bably now,  as  it  has  in  the  past,  appeal  more  forcibly  to 
the  mind  of  the  ordinary  man ;  and  we  must  not  despise 
any  inducement,  which  will  lead  to  the  furtherance  of 
the  object  to  be  gained,  provided  the  motives  are  not  in 
themselves  sordid. 

The  study  of  science,  with  the  express  object  of  securing 
wealth  and  fame,  is  not  likely  to  secure  either.  The  old 
story  of  the  desire  of  King  Solomon  is  often  fulfilled  in 
our  day.  Solomon's  request  was, '  Give  me  now  wisdom 
and  knowledge ' ;  and  he  was  answered,  '  Wisdom  and 
knowledge  is  granted  unto  thee,  and  I  will  give  thee 
riches  and  wealth  and  honour.'  The  reason  why  an 
attempt  to  utilise  science  for  the  attainment  of  wealth 
often  fails  is  a  simple  one.  It  is  due  to  the  unfortunate 
circumstance  that  the  human  mind  is  not  omniscient. 
No  man,  beginning  a  research,  can  know  to  what  it  will 
ultimately  lead.  It  will  certainly,  if  rightly  pursued, 
lead  to  knowledge ;  but  whether  it  will  bring  riches  and 
fame  is  beyond  his  ken.  There  have  been,  however, 
researches  expressly  directed  to  some  specific  object, 
which  have  succeeded  in  their  purpose;  and  we  shall 
see  later  how  the  discovery  of  principles  which  led  to 
the  invention  of  the  safety-lamp  by  Sir  Humphry  Davy 
illustrates  this.  But  as  a  rule,  those  chemists  who  have 


THE  GREAT  LONDON  CHEMISTS  21 

achieved  for  themselves  immortal  fame  have  striven 
after  the  nobler  goal — the  increase  of  the  sum  of  human 
knowledge.  It  is  to  the  lives  of  some  of  those,  who  have 
been  more  or  less  connected  with  London,  that  I  ask  your 
attention.  May  those  of  us  who  follow,  at  however  -far  a 
distance,  profit  by  their  example ! 

In  the  olden  days,  science,  as  we  know  it  now,  was 
non-existent.  The  minds  of  most  men  who  were  free 
from  the  thraldom  of  incessant  labour  were  occupied 
with  war  or  statecraft  as  a  business,  and  with  the  chase 
as  a  recreation.  Those  to  whom  such  pursuits,  from 
circumstances  or  mental  habit,  were  repugnant,  found 
occupation  in  history,  poetry,  philosophical  discussion, 
or  religion.  It  is  true,  speculation  on  the  nature  of  the 
world  around  them  was  indulged  in  by  some;  but  they 
were  guided  in  their  views  by  their  opinion  rather  of  what 
ought  to  be,  than  what  is.  The  attitude  of  the  modern 
mind  is  more  humble.  We  no  longer  believe  that  we 
share  enough  of  the  creative  power  to  enable  us  to 
construct  a  system  of  the  universe;  we  are  content  if 
we  are  able,  in  however  modest  a  way,  to  interpret 
nature,  and  we  call  to  our  aid  experiment,  as  a  means  of 
questioning  nature.  We  are  prompt  in  communicating 
our  knowledge  to  others,  and  we  expect  their  aid  and 
look  for  their  criticism.  In  former  days,  the  language 
of  mystery  was  employed.  It  concealed  secrets  too 
precious  to  be  laid  bare  to  the  vulgar  crowd.  '  In  those 
days/  to  quote  the  words  of  Dr.  Samuel  Brown,1  'the 
metals  were  suns  and  moons,  kings  and  queens,  red 
bridegrooms  and  lily  brides.  Gold  was  Apollo,  "  sun  of 
the  lofty  dome";  silver,  Diana,  the  fair  moon  of  his 
unresting  career,  and  chased  him  meekly  through  the 
celestial  grove ;  quicksilver  was  the  wing-footed  Mercury, 

1  Dr.  Samuel  Brown's  Essays. 


22    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Herald  of  the  Gods,  "new-lighted  on  a  heaven-kissing 
hill " ;  iron  was  the  ruddy-eyed  Mars,  in  panoply  complete ; 
lead  was  heavy-lidded  Saturn,  "  quiet  as  a  stone,"  within 
the  tangled  forest  of  material  forms ;  tin  was  the  Diabolus 
Metallorum,  a  very  devil  among  the  metals,  and  so  forth 
in  not  unmeaning  mystery. 

'  There  were  flying  birds,  green  dragons,  and  red  lions. 
There  were  virginal  fountains,  royal  baths,  and  waters  of 
life.  There  were  salts  of  wisdom,  and  essential  spirits  so 
fine  and  volatile,  that  drop  after  drop,  let  fall  from  the 
lip  of  the  wonderful  phial  that  contained  them,  could 
never  reach  the  ground.  There  was  the  powder  of 
attraction  which  drew  all  men  and  women  after  its 
fortunate  possessor ;  and  the  alcahest,  or  universal  solvent 
and  noli-me-tangere  of  essences.  There  was  the  grand 
elixir  that  conferred  undying  youth  on  the  glorious 
mortal  who  was  pure  and  brave  enough  to  kiss  and 
quaff  the  golden  wavelet  as  it  mantled  o'er  the  cup  of 
life — the  fortunate  Endymion  of  a  new  mythology.  There 
were  the  Philosophical  stone,  and  the  Philosopher's  stone ; 
the  former  the  art  and  practice,  the  latter  the  theory 
and  idea,  of  turning  baser  natures  into  nobler ;  the  theory 
and  practice  of  exaltation.  The  Philosophical  stone  was 
younger  than  the  elements,  yet  at  her  virgin  touch  the 
grossest  calx  among  them  all  would  blush  before  her  into 
perfect  gold.  The  Philosopher's  stone  was  the  first-born 
of  all  things,  and  older  than  the  king  of  metals. — In  a 
word,  there  was  an  interminable  imbroglio  of  a  few  of 
the  hard-won  facts  of  nature,  a  multitude  of  traditionary 
processes  and  results,  several  very  just  analogies,  some 
most  fantastical  notions,  one  or  two  profound,  but  intract- 
able ideas,  a  haze  of  philosophical  mysticism,  and  an 
under-current  of  fervid  religiosity.' 

Such  conceptions  ruled  the  minds  of  philosophers,  as 
they  loved  to  call  themselves,  until  the  middle  of  the 


THE  GREAT  LONDON  CHEMISTS  23 

seventeenth  century.  But  the  practice  of  interrogating 
nature  by  experiment  had  sprung  up,  and  was  soon 
destined  to  bear  good  fruit.  Although  these  notions  of 
matter  and  its  elementary  forms  lingered  on  until  a  much 
later  date,  and  indeed  are  not  wholly  extinct  at  the  present 
day,  they  received  their  first  great  blow  about  this  time ; 
the  first  brunt  of  an  attack  which  was  destined  ultimately 
to  overthrow  them. 

This  attack  was  made  by  Boyle.  The  spirit  in  which 
he  approached  the  hostile  ranks  is  best  given  in  his  own 
words:  'For  I  am  wont  to  judge  of  opinions,  as  of  coins; 
I  consider  much  less  in  any  one  that  I  am  to  receive 
whose  inscription  it  bears,  than  what  metal  'tis  made  of. 
'Tis  indifferent  enough  to  me  whether  'twas  stamped 
many  years  or  ages  since,  or  came  but  yesterday  from 
the  mint.  Nor  do  I  regard  how  many  or  how  few  hands 
it  has  passed  through,  provided  I  know  by  the  touchstone 
whether  or  no  it  be  genuine,  and  does  or  does  not  deserve 
to  have  been  current.  For  if,  upon  due  proof,  it  appears 
to  be  good,  its  having  been  long  and  by  many  received 
for  such  will  not  tempt  me  to  refuse  it ;  but  if  I  find  it 
counterfeit,  neither  the  Prince's  image  nor  superscription, 
nor  its  date,  nor  the  multitude  of  hands  it  has  passed 
through,  will  engage  me  to  receive  it.  And  one  dis- 
favouring trial,  well  made,  will  much  more  discredit  it 
with  me,  than  all  those  spurious  things  I  have  named 
can  recommend  it.' 

In  this  spirit  the  '  Sceptical  Chymist,  or  considerations 
upon  the  experiments  usually  produced  in  favour  of 
the  four  elements,  and  of  the  three  chymical  principles 
of  the  mixed  bodies'  was  written.  In  it,  the  various 
theories  of  matter,  which,  like  a  river  rising  in  the 
remotest  recesses  of  time  had  gathered  tributaries  as  it 
flowed  and  presented  a  formidable  flood  in  Boyle's  days, 
were  searchingly  criticised.  Every  postulate  was  examined ; 


24    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

if  possible,  experimentally  tested;  if  true,  kept;  if  false, 
rejected. 

Thus,  early  in  the  book,  we  meet  with  the  phrase,  long 
accepted  as  true,  ffomogenea  congregare ;  that  is,  'Like 
draws  to  like.'  This  Boyle  disproved  by  showing  that 
liquids,  like  alcohol  and  water,  alike  in  being  colourless 
and  transparent,  although  they  mix  with  each  other,  may 
be  easily  separated  by  freezing;  for,  when  cooled,  the 
water  freezes,  leaving  the  alcohol  unfrozen.  Here  we  find 
the  first  record  of  experiments  on  a  subject  which,  in 
Raoult's  hands,  yielded  such  extraordinarily  important 
results.  Another  of  Boyle's  arguments  is,  that  although 
liquids  and  gases  mix  respectively  with  each  other,  yet 
solids  show  no  such  tendency,  and  do  not  even  cohere, 
except  in  cases  where  the  cohesion  can  be  explained 
by  the  form  of  the  solid,  and  the  consequent  exertion  of 
atmospheric  pressure. 

After  making  a  number  of  such  attacks,  Boyle  proceeds 
to  consider  the  hypothesis  at  that  time  all-prevalent  and 
universally  accepted,  of  the  elements  salt,  sulphur,  and 
mercury.  He  opens  two  distinct  lines  of  attack.  His 
first  may  be  stated  thus :  If  all  substances  are  composed 
of  salt,  sulphur,  and  mercury,  and  if  vegetable  and  animal 
substances  contain,  as  is  stated,  much  mercury,  little 
sulphur,  and  less  salt,  then  it  is  desirable  to  show  that  a 
vegetable  may  be  constructed  of  a  substance  containing 
none  of  these  principles,  but  only  of  water,  which  was 
then  sometimes  termed  '  phlegm/  and  was  ranked  among 
the  elements.  This  he  attempted  by  growing  a  '  pompion ' 
in  a  weighed  quantity  of  earth,  and  after  the  pumpkin 
had  grown,  he  showed  it  to  consist  of  water,  by  distilling 
it ;  and  by  weighing  the  earth,  he  proved  that  it  had  not 
lost  weight.  He  then  turns  to  the  c  vulgar  spagyrist/  and 
triumphantly  challenges  the  truth  of  his  theory.  It  is 
now  known  that  the  elements  carbon  and  nitrogen,  and 


THE  GREAT  LONDON  CHEMISTS  25 

others  in  small  quantity,  must  be  added  to  those  contained 
in  water  to  produce  a  '  pompion ' ;  but  it  was  a  great  step 
to  show  that  no  salt,  sulphur,  or  mercury  were  necessary. 
Boyle  viewed  the  '  pompion '  as  simply  transmuted  water. 
He  quotes  from  M.  de  Roche,  who  stated  that  he  had 
transmuted  earth  into  water,  and  vice  versa.  Of  the 
correctness  of  M.  de  Roche's  opinion,  he  is  not  quite 
sure,  but  he  attaches  a  certain  amount  of  weight  to  it. 

His  second  line  of  attack  is  to  prove  that  the  so-called 
elements  are  themselves  further  resolvable.  And  begin- 
ning with  sulphur,  he  points  out  that  what  the  chymists 
understand  by  sulphur  has  not  always  the  same  properties. 
It  is,  however,  always  inflammable.  Sulphur,  in  the  then 
accepted  meaning  of  the  word,  was  the  inflammable 
portion  obtained  on  distilling  an  animal  or  vegetable 
substance;  mercury,  another  portion,  not  miscible  with 
the  sulphur;  but  uninflammable,  and  having  taste;  the 
residue  on  incineration,  or,  as  it  was  termed,  the  caput 
mortuum,  was  salt.  In  an  old  writing  on  the  subject, 
salt  is  said  to  be  the  basis  of  solidity  and  permanency 
in  compound  bodies ;  oil  or  sulphur  (the  two  words  came 
to  have  nearly  the  same  meaning)  serves  the  purpose  of 
making  the  mass  more  tenacious ;  mercury  is  to  leaven 
and  to  promote  the  ingredients,  and  earth  is  to  soak  and 
dry  up  the  water  in  which  the  salt  is  dissolved. 

We  note  here  a  change  in  the  manner  of  regarding 
elements.  They  are  no  longer  principles,  or  abstract 
qualities  of  matter,  but  they  exist  in  the  matter,  and  can 
be  extracted  from  it  by  suitable  processes.  Their  number 
varied ;  and  phlegm  or  water  was  now  accepted  as  elemen- 
tary, now  rejected,  as  suited  the  purpose  of  the  theorist. 
Boyle  clearly  showed  that  these  elements  had  not  always 
the  same  properties;  that  the  sulphur  and  mercury  not 
only  differed  in  every  respect  from  brimstone  and  quick- 
silver, but  that  one  variety,  obtained  by  distilling  wood, 


26    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

differed  from  that  obtained  by  submitting  bones  to  the 
same  process.  He  clinched  his  point  by  distilling  the 
distillates  themselves  in  turn — in  fact  by  performing  what 
we  now  call  a  '  fractional  distillation ' — and  showed  that 
it  was  possible  to  divide  them  in  turn  into  several  liquids, 
differing  from  each  other  in  properties.  In  this  he  antici- 
pated a  process  now  practised  on  a  very  large  scale,  namely 
the  manufacture  of  vinegar  from  wood,  which  he  success- 
fully separated  from  wood-spirit  and  tar. 

Almost  all  research,  before  Boyle's  time,  employed  two 
processes,  ignition  or  heating  in  contact  with  air,  and  dis- 
tillation, or  heating  in  a  vessel  of  irregular  shape,  named 
an  alembic,  leading  the  vapours  through  a  cooled  tube, 
still  called  a  worm,  and  collecting  the  liquefied  product  in 
a  pear-shaped  vessel,  named  a  receiver.  Heat  was  assumed 
to  be  the  universal  resolver  of  bodies ;  and  the  products 
of  the  action  of  heat  on  compounds  were  accepted  as 
elements.  Boyle  doubted  this;  he  questioned  whether 
the  products  obtained  on  distillation  were  pre-existent  in 
the  substances  distilled,  as  the  theory  of  elements  would 
require.  He  found  that  on  distillation  the  same  substances 
are  not  always  produced,  nor  the  same  number ;  and  he 
demonstrated  that  these  products  themselves  are  not  pure 
or  elementary  bodies,  but '  mixts.'  He  says :  '  It  is  to  be 
doubted  whether  or  no  there  be  any  determinate  number 
of  elements,  or  if  you  please,  whether  all  compound  bodies 
do  consist  of  the  same  number  of  elementary  principles 
or  ingredients.' 

But  Boyle  was  not  merely  a  destroyer ;  he  also,  if  not 
in  so  orderly  a  manner,  attempted  to  construct  a  theory 
of  his  own.  He  appears  to  have  held  the  notion  of  a 
universal  matter,  and  to  have  conceived  the  different 
varieties  to  be  due,  not  to  the  presence  of  separable  pro- 
perties, but  to  the  form  and  motion  of  its  minute  portions. 
In  supporting  this  doctrine  against  the  theories  prevalent 


THE  GREAT  LONDON  CHEMISTS  27 

in  his  time,  he  says :  '  I  demand  also,  from  which  of  the 
chymical  principles  motion  flows,  which  yet  is  an  affection 
of  matter  much  more  general  than  can  be  deduced  from 
any  of  the  three  chymical  principles.'  In  an  essay  entitled 
'  The  history  of  Fluidity  and  Firmness,'  he  endeavours  with 
some  success  to  show  that  all  bodies,  even  those  which 
appear  most  rigid,  are  in  motion.  For  example,  he  points 
out  that  the  diamond  when  rubbed  shines  in  the  dark, 
and  in  conformity  with  our  present  views,  attributes  that 
to  molecular  motion.  He  also  notices  that  all  bodies  ex- 
pand by  heat,  and  is  inclined  to  ascribe  the  magnetisation 
of  steel  to  the  motion  of  its  minute  particles.  He  attri- 
butes the  varying  properties  of  matter  to  motion  and 
rest.  In  yet  another  passage,  he  supposes  the  action  of 
acids  on  metals  to  be  due  to  the  pointed  shape  of  their 
atoms,  which,  by  inserting  themselves  between  the  more 
rounded  particles  of  the  metal,  wedge  them  asunder,  and 
themselves  become  blunt  during  the  process. 

It  is  difficult  to  overestimate  the  value  of  Boyle's 
labours  in  the  field  of  chemistry.  Although  he  was  the 
first  to  proclaim  that  chemistry  is  independent  of  any  art, 
and  must  be  regarded  as  part  of  the  great  field  of  nature, 
yet  the  practical  benefit  which  has  accrued  to  mankind 
through  Boyle's  theoretical  as  well  as  his  practical  work 
is  incalculable.  It  was  not  until  after  his  time  that  it 
was  possible  to  construct  a  theory  explaining  the  rule-of- 
thumb  methods  of  manufacture  which  were  formerly 
employed,  and  to  render  improvement  and  discovery  no 
longer  a  matter  of  chance,  but  of  reasoning.  The  whole 
progress  of  modern  manufacture  due  to  the  elaboration 
of  scientific  discoveries,  themselves  the  result,  not  of  hap- 
hazard trial,  but  of  careful  and  systematic  investigation, 
sufficiently  attests  the  benefit  conferred  by  him  in  the 
practical  application  of  scientific  principles. 

Time  would  fail  to  tell  of  Boyle's  well-known  memoir 


28    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

'  Touching  the  Spring  of  the  Air/  in  which  he  describes 
experiments  proving  that  a  volume  of  air  under  a  pressure 
of  two  pounds  occupies  exactly  half  the  volume  that  it 
does  under  a  pressure  of  one  pound.  This,  although  not 
absolutely  true,  is  yet  sufficiently  exact  to  be  generalised 
into  a  law,  which  is  known  by  Boyle's  name.  He  finds  a 
reason  for  this  '  spring '  in  premising  that '  the  air  abounds 
in  elastic  particles,  which  being  pressed  together  by  their 
own  weight  constantly  endeavour  to  expand  and  free 
themselves  from  that  force ;  as  wool,  for  example,  resists 
the  hand  that  squeezes  it,  and  contracts  its  dimensions ; 
but  recovers  them  when  the  hand  opens,  and  endeavours 
at  it  even  while  that  is  shut.' 

In  truth  Boyle  delighted  in  mechanical  explanations. 
The  titles  of  his  papers  attest  this.  We  find,  'The 
Mechanical  Production  of  Magnetism ' ;  '  The  Mechanical 
Production  of  Electricity';  'The  Mechanical  Causes  of 
Precipitation';  'The  Mechanical  Origin  of  Corrosiveness 
and  Corrosibility ' ;  and  even,  '  The  Mechanical  Produc- 
tion of  Tastes  and  Colours.'  The  series  finishes  with  '  The 
Mechanical  Origin  of  Heat  and  Cold.'  To  produce  heat 
it  is  necessary '  that  the  moving  particles  should  be  small'; 
and  '  agitation  is  requisite  to  heat ' ; — in  fact,  a  statement, 
in  language  of  the  time,  of  modern  views.  In  accounting 
for  the  decomposition  of  bodies  by  heat,  his  words  are : 
'  It  rather  seems  that  the  true  and  genuine  property  of 
heat  is  to  set  amoving  arid  thereby  dissociate  the  particles 
of  matter.' 

In  spite  of  Boyle's  numerous  attempts  to  account  for 
natural  phenomena  in  terms  of  matter  and  motion,  his 
modesty  led  him  to  make  this  statement :  '  Having  met 
with  many  things  of  which  I  could  give  myself  no  probable 
cause,  and  some  things  to  which  several  causes  may  be 
assigned,  so  differing  as  not  to  be  able  to  agree  in  anything 
unless  in  their  all  being  probable  enough;.!  have  often 


THE  GREAT  LONDON  CHEMISTS  29 

found  such  difficulty  in  searching  into  the  cause  and 
manner  of  things,  and  I  am  so  sensible  of  my  own  disability 
to  surmount  these  difficulties,  that  I  dare  speak  posi- 
tively of  very  few  things  except  of  matters  of  fact.'  This, 
I  think,  is  in  the  main  still  our  position. 

Boyle's  claim  to  rank  as  a  'Great  London  Chemist' 
rests  upon  his  having  taken  up  his  residence  here  from 
the  year  1668,  until  his  death,  which  took  place  on  the 
last  day  of  the  year  1691,  in  the  sixty-fifth  year  of  his 
age.  But  he  was  not  a  Londoner  by  birth.  He  was  an 
Irishman,  born  at  Lismore  in  County  Waterford,  and  of 
noble  parentage,  for  he  was  the  seventh  son,  and  the 
fourteenth  child,  of  the  Earl  of  Cork.  He  was  educated  as 
a  child  at  home ;  but  at  the  age  of  eight  he  was  sent  to 
Eton,  where,  as  he  says, '  he  lost  much  of  that  Latin  he 
had  got ;  for  he  was  so  addicted  to  the  more  solid  parts  of 
knowledge,  that  he  hated  the  study  of  bare  words  natur- 
ally.' At  the  age  of  eleven  (they  were  precocious  in  those 
days)  his  career  at  Eton  was  over ;  and  he  was  sent  with 
a  French  tutor,  along  with  his  brother,  to  Geneva,  where 
he  pursued  his  studies  for  twenty-one  months,  and  then 
went  to  Italy.  There  he  stayed  until  1642;  when  his 
father's  finances  having  become  embarrassed,  owing  to  the 
breaking  out  of  the  great  Irish  rebellion,  Boyle  returned 
home,  to  find  his  father  dead.  Two  estates  had  been  left 
to  him ;  one  at  Stalbridge,  in  Dorsetshire,  where  he  pro- 
ceeded to  reside.  In  1654,  when  twenty-seven  years  of 
age,  he  removed  to  Oxford,  in  order  to  associate  himself 
with  a  number  of  men  who  had  united  themselves  into  a 
society,  under  the  name  of  the  'Philosophical  College/ 
This  society  afterwards  moved  its  headquarters  to  London ; 
and  in  1663  it  was  incorporated  by  Charles  n.,  under  the 
name  of  the  '  Royal  Society  of  London/  its  object  being 
the  '  Promotion  of  Natural  Knowledge.' 

Boyle's  name  is  frequently  mentioned  in  the  first  few 


30    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

volumes  of '  The  Transactions.'  Thus  we  find  on  January  2, 
1601,  that  'Mr.  Boyle  was  requested  to  bring  in  his 
cylinder,  and  to  show  at  his  best  convenience  the  experi- 
ment of  the  air ' ;  but  his  convenience  was  long  in  arriv- 
ing, for  on  March  the  20th  '  Mr.  Boyle  was  requested  to 
remember  his  experiment  of  the  air,'  and  on  April  1  '  he 
was  desired  to  hasten  his  intended  alteration  of  his  air- 
pump.'  On  May  15,  'Mr.  Boyle  presented  the  Society 
with  his  engine,'  and  with  it  numerous  experiments 
were  made  in  the  presence  of  members  of  the  Society. 
In  such  '  philosophical '  pursuits  he  spent  his  uneventful 
life;  and,  to  quote  his  own  words,  from  a  biographical 
sketch  drawn  up  by  himself  at  an  advanced  period  of  his 
life,  he  says :  '  To  be  such  parents'  son,  and  not  their 
eldest,  was  a  happiness  that  our  Philarethes  [a  lover  of 
virtue — himself]  would  mention  with  great  expressions  of 
gratitude ;  his  birth  so  suiting  his  inclinations  and  designs, 
that  had  he  been  permitted  an  election,  his  choice  would 
scarce  have  altered  God's  discernment.' 

Cavendish,  like  Boyle,  was  also  of  noble  birth.  He  was 
the  son  of  Lord  Charles  Cavendish,  himself  the  third  son 
of  the  second  Duke  of  Devonshire.  His  mother  was  Lady 
Anne  Grey,  fourth  daughter  of  Henry,  Duke  of  Kent. 
But  except  in  the  fact  of  their  both  being  of  the  higher 
rank  of  society,  and  in  their  both  being  addicted  to  the 
pursuit  of  science,  they  have  little  in  common.  Boyle's 
mind  roamed  over  the  whole  domain  of  nature ;  his  writ- 
ings treat  of  religious,  philosophical,  and  scientific  subjects 
with  a  fulness  and  lack  of  mental  reserve  which  testify 
to  his  frank,  transparent  character.  His  motto  was  Nihil 
humanum  a  me  alienum  puto ;  and  he  carried  this  motto 
into  his  life  and  work.  Cavendish,  on  the  other  hand, 
was  by  nature  very  shy  and  reserved ;  he  had  no  friends, 
and  few  acquaintances;  and  instead  of  discussing  the 
whole  of  nature,  as  did  Boyle,  he  limited  himself  to  the 


THE  GREAT  LONDON  CHEMISTS  31 

investigation  of  a  few  problems  of  first-rate  importance. 
His  work  is  characterised  by  the  utmost  accuracy  and 
elegance ;  and  he  was  cautious  to  an  extreme  in  announc- 
ing his  conclusions.  Both  types  of  mind  have  their  good 
side  ;  but  in  their  case  one  might  have  wished  for  a  little 
more  moderation.  Had  Boyle  not  been  so  many-sided,  he 
might  have  advanced  science  more  by  accurate  experi- 
mental work ;  and  had  Cavendish  not  been  so  reserved, 
he  would  have  done  more  good  to  his  contemporaries,  and 
he  would  certainly  have  been  a  happier  man.  Neither 
was  married;  and  it  is  perhaps  legitimate  to  draw  the 
conclusion  that  man's  nature  does  not  culminate  in  its 
best  without  the  influence  of  a  helpmeet. 

Like  Boyle's,  Henry  Cavendish's  life  was  an  uneventful 
one,  and  may  be  told  in  a  few  words.  He  was  born  on  the 
10th  October  1731,  at  Nice,  where  his  mother  had  gone 
for  her  health.  She  died  when  he  was  two  years  old.  In 
1742,  he  became  a  pupil  of  Dr.  Newcome,  at  Hackney 
School,  where  he  stayed  until  1749 ;  in  that  year,  he 
matriculated  at  Cambridge,  and  entered  as  a  student  at 
Peterhouse.  In  1753,  he  left  without  taking  his  degree; 
he  probably  went  to  London ;  but  all  details  of  his  life  are 
lacking  for  the  next  ten  years,  though  it  is  probable  that 
he  spent  the  major  part  of  his  time  in  mathematical  and 
physical  studies,  and  in  research  in  the  stables  belonging 
to  his  father's  town  house,  which  he  had  fitted  up  as  a 
laboratory.  It  was  not  until  1766  that  he  summoned  up 
resolution  enough  to  publish;  although  his  note-books 
show  that  in  1764  he  had  begun  to  make  experiments 
which  would  have  been  well  worth  recording.  From  that 
time  forward,  until  1809,  the  year  before  his  death,  his 
papers  appeared  in  constant  succession.  There  was  little 
interruption  to  this  incessant  work,  unless  we  consider  a 
series  of  journeys  made  through  various  parts  of  England 
and  Wales  with  the  object  of  studying  the  geology  of  the 


32    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

country,  and  the  manufactures  carried  on  in  the  various 
industrial  centres,  as  a  species  of  holiday.  There  was 
no  weekly  interruptions  to  his  labours;  Sunday  as  well 
as  weekday  was  devoted  to  research,  and  so  the  years 
glided  past.  During  his  father's  lifetime,  he  is  said  to 
have  had  an  income  of  £500  a  year ;  but  at  his  father's 
death  in  1783,  and  afterwards,  owing  to  the  legacy  of  an 
aunt,  he  became  possessed  of  enormous  riches.  Indeed, 
M.  Biot,  in  pronouncing  a  biographical  oration  on  Caven- 
dish, used  the  phrase :  '  II  etait  le  plus  riche  de  tons  les 
savants,  et  probablement  aussi,  le  plus  savant  de  tous  les 
riches? 

His  town  house  was  at  the  corner  of  Montague  Place 
and  Gower  Street ;  visitors,  however,  were  rarely  ad- 
mitted ;  and  Cavendish  kept  his  library  for  his  own  use 
and  for  that  of  the  scientific  public  in  a  separate  house  in 
Dean  Street,  Soho.  To  this  library  he  went  for  his  own 
books,  signing  a  formal  receipt,  as  one  would  do  at  a 
public  library,  for  each  one  borrowed. 

His  laboratory  was  a  villa  at  Clapham.  The  upper 
rooms  were  an  astronomical  observatory.  Here  he 
occasionally  entertained  friends,  but  in  an  unostentatious 
way.  His  standing  dish  was  a  leg  of  mutton.  It  is 
related  that  on  one  occasion,  when  the  unprecedented 
number  of  five  guests  had  been  invited,  his  housekeeper 
ventured  to  point  out  that  one  leg  of  mutton  would  be 
insufficient  fare  for  so  many ;  his  answer  was,  '  Well,  then, 
get  two.'  Several  of  his  contemporaries  have  left  a 
record  of  their  personal  impressions  of  him.  Professor 
Playfair  described  him  as  of  an  awkward  appearance, 
without  the  look  of  a  man  of  rank.  He  spoke  very 
seldom,  and  then  with  great  difficulty  and  hesitation,  but 
exceedingly  to  the  purpose,  his  remarks  either  displaying 
some  excellent  information,  or  drawing  some  important 
conclusion.  An  Austrian  gentleman  to  whom  he  had 


THE  GREAT  LONDON  CHEMISTS  33 

been  introduced,  after  the  fashion  of  his  country,  assured 
him  that  his  principal  reason  for  coming  to  London  was 
to  see  and  converse  with  one  of  the  greatest  ornaments  of 
his  age,  and  one  of  the  most  illustrious  philosophers  that 
ever  existed.  To  all  these  high-flown  speeches  Mr.  Caven- 
dish answered  not  a  word,  but  stood  with  his  eyes  cast 
down,  quite  abashed  and  confounded.  At  last,  spying  an 
opening  in  the  crowd,  he  darted  through  it  with  all  the 
speed  he  could  muster,  nor  did  he  stop  until  he  reached 
his  carriage,  which  drove  him  directly  home.  Sir  Hum- 
phry Davy  said  of  him :  '  His  voice  was  squeaking,  his 
manner  nervous ;  he  was  afraid  of  strangers,  and  seemed, 
when  embarrassed,  even  to  articulate  with  difficulty.  He 
wore  the  costume  of  our  grandfathers;  was  enormously 
rich,  but  made  no  use  of  his  wealth.'  And  Lord 
Brougham's  recollection  was  that  he  would  often  leave 
the  place  where  he  was  addressed,  and  leave  it  abruptly, 
with  a  kind  of  cry  or  ejaculation,  as  if  scared  and  dis- 
turbed. '  I  recollect/  said  Lord  Brougham, '  the  shrill  cry 
he  uttered,  as  he  shuffled  quickly  from  room  to  room, 
seeming  to  be  annoyed  if  looked  at,  but  sometimes 
approaching  to  hear  what  was  passing  among  others/ 

On  occasion,  he  was  not  ungenerous,  although  the 
thought  of  giving  did  not  occur  to  him.  When  dining 
one  evening  at  the  Royal  Society  Club,  some  one  present 
mentioned  the  name  of  a  gentleman  who  had  previously 
acted  as  a  temporary  librarian  in  his  library.  Mr.  Caven- 
dish said, '  Ah  !  poor  fellow,  how  does  he  do  ?  How  does 
he  get  on ? '  'I  fear  very  indifferently/  said  this  person. 
'  I  am  sorry  for  it/  said  Mr.  Cavendish.  '  We  had  hopes 
that  you  would  have  done  something  for  him,  sir/  '  Me, 
me,  me,  what  could  I  do  ? '  'A  little  annuity  for  his  life ; 
he  is  not  in  the  best  of  health.'  'Well,  well,  well,  a 
cheque  for  £10,000,  would  that  do  ? '  '0  sir,  more 
than  sufficient,  more  than  sufficient/ 


34    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Solitary  he  lived,  and  solitary  was  his  death.  Having 
been  ill  for  several  days,  his  valet  was  called  to  his  bed- 
side, and  told  to  summon  Lord  George  Cavendish,  as  soon 
as  he  should  be  dead.  In  about  half  an  hour  he  again 
summoned  the  servant,  and  made  him  repeat  the 
message.  He  then  said,  '  Right.  Give  me  the  lavender 
water.  Go.'  Half  an  hour  later  the  servant  returned  to 
his  room,  and  found  that  he  had  expired. 

If  Boyle  found  interest  in  all  things  human,  Cavendish 
appeared  to  take  no  thought  of  anything,  except 
phenomena.  As  his  biographer,  Dr.  George  Wilson,  said, 
his  motto  was  Panta  metro,  kai  arithmo,  kai  stathmo 
(Tlavra  /jLerpy,  Kai  apiO/jbw,  Kai  araOfjiq)).  This  we  shall 
now  learn,  from  a  short  consideration  of  his  work. 

Cavendish's  earlier  work  is  only  to  be  found  in  his  un- 
published papers.  It  appeared  to  have  been  his  habit, 
for  some  time,  to  write  an  account  of  his  experiments, 
without  any  intention  of  bringing  them  to  the  notice  of 
the  public.  An  account  of  two  long  investigations  was 
found  among  his  papers,  after  his  death,  of  a  date  con- 
siderably prior  to  that  on  which  his  first  memoir 
appeared  in  the  Philosophical  Transactions.  The  first 
of  these  deals  with  the  differences  between  'regulus  of 
arsenic'  (metallic  arsenic)  and  its  two  oxides.  He  con- 
cluded that  arsenic  oxide  was  '  more  thoroughly  deprived 
of  its  phlogiston '  (in  modern  language,  more  thoroughly 
oxidised)  than  arsenious  oxide;  and  the  latter,  than 
arsenic  itself.  The  paper  also  contains  speculations  on 
the  nature  of  the  red  fumes  obtained  in  the  conversion 
of  arsenious  to  arsenic  oxide  by  means  of  nitric  acid ; 
speculations  which  were  afterwards  to  bear  rich  fruit,  in 
his  work  on  the  composition  of  air. 

Another  of  his  unpublished  researches  deals  with  heat. 
Cavendish  discovered  independently  the  laws  of  specific 
heat ;  and  he  collected  tables  of  the  specific  heats  of  many 


THE  GREAT  LONDON  CHEMISTS  35 

substances.  He  also  was  acquainted  with  what  Black 
termed  '  latent  heat/  that  is,  the  heat  absorbed  during  the 
evaporation  of  liquids,  or  which  is  evolved  during  the 
condensation  of  gases  or  vapours,  or  the  solidification  of 
liquids. 

As  this  essay  deals  with  Cavendish  as  a  chemist,  I  shall 
treat  very  shortly  of  his  physical  work.  One  of  the  most 
important  of  his  investigations  has  reference  to  the 
cause  of  the  shock  given  by  that  curious  fish  the 
torpedo.  By  constructing  a  species  of  artificial  torpedo, 
he  proved  that  the  shock  was  due  to  an  electric  discharge  ; 
and  what  is  more,  he  was  the  first  to  distinguish  between 
electric  quantity  and  electric  intensity.  Indeed,  these 
terms  are  due  to  him,  as  Faraday  has  acknowledged. 

In  1783,  1786,  and  1788,  he  published  three  papers  on 
freezing,  in  which  his  views  on  the  nature  of  heat  were 
expounded.  The  first  of  these  deals  with  the  freezing  of 
mercury ;  the  second  and  third,  with  the  congelation  of 
the  mineral  acids,  and  of  alcohol.  He  objected  to  Black's 
expression,  '  the  evolution,  or  setting  free  of  latent  heat/ 
as  involving  an  hypothesis  that  the  heat  of  bodies  is 
owing  to  their  containing  more  or  less  of  a  substance 
called  the  matter  of  heat.  He  preferred  to  adopt  Boyle's 
and  Sir  Isaac  Newton's  supposition  that  heat  consists  in 
the  internal  motion  of  the  particles  of  bodies.  And  he 
therefore  uses  the  expression  '  heat  is  generated.' 

An  interesting  part  of  the  last  of  these  papers  is  a 
passage  in  which  he  anticipates  Richter's  tables  of  the 
equivalents  of  the  acids  and  bases,  not  by  any  elaborate 
disquisition,  but  as  a  device  for  estimating  the  strength  of 
sulphuric  acid.  In  1788  he  wrote :  '  The  method  I  used 
was  to  find  the  weight  of  the  plumbum  vitriolatum  formed 
by  the  addition  of  sugar  of  lead,  and  from  thence  to  com- 
pute the  strength,  on  the  supposition  that  a  quantity  of 
oil  of  vitriol,  sufficient  to  produce  100  parts  of  plumbum 


36    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

vitriolatum,  will  dissolve  33  of  marble;  as  I  found  by 
experiment  that  so  much  oil  of  vitriol  would  saturate  as 
much  fixed  alkali  as  a  quantity  of  nitrous  acid  sufficient 
to  dissolve  33  of  marble.'  Richter's  tables  were  published 
in  1792.  Cavendish's  remarks  involve  a  knowledge  of 
fixity  of  proportion,  and  also  of  reciprocal  proportions; 
doctrines  which  were  after  nearly  twenty  years  pro- 
pounded by  Dalton. 

Perhaps  the  most  important  piece  of  physical  work 
ever  performed  was  Cavendish's  determination  of  the 
constant  of  gravitation,  or  as  it  is  often  called, '  the  weight 
of  the  earth.'  The  experiment  is  usually  spoken  of  as 
the  'Cavendish  experiment,'  although  the  method  of 
executing  it  was  first  suggested  by  the  Rev.  John  Mitchell. 
A  delicate  torsion  balance,  suspended  by  a  wire,  had 
leaden  balls  suspended  at  each  end.  Two  heavy  spherical 
masses  of  metal  were  brought  near  the  balls,  so  that  their 
attraction  tended  to  draw  the  two  balls  aside.  The  de- 
viation of  the  arms  was  observed,  or  calculated  from  the 
time  of  vibration ;  and  from  the  data  found,  it  is  easy  to 
calculate  the  attraction  of  a  sphere  of  water,  equal  in 
mass  to  the  ball  or  a  similar  ball  resting  on  its  surface ; 
and  so  to  determine  the  density  of  the  earth,  knowing  the 
attraction  which  it  exerts  on  the  ball.  The  results 
obtained  compared  very  favourably  with  the  best  results 
obtained  by  other  observers,  using  the  utmost  precau- 
tions ;  and  it  is  a  very  remarkable  instance  of  Cavendish's 
experimental  skill  and  ingenuity. 

We  have  here  to  consider  more  particularly  Caven- 
dish's chemical  work.  It  was  of  the  highest  order,  and 
bears  the  imprint  of  a  master  mind,  guiding  a  master 
hand. 

Before  Black's  time,  the  word  *  gas '  had  no  plural. 
Indeed,  what  we  now  know  as  a  gas  was  set  down  as  a 
modification  of  ordinary  air.  Black,  however,  proved  that 


THE  GREAT  LONDON  CHEMISTS  37 

a  gas  could  be  contained  in  a  solid  state,  as  for  instance 
in  carbonate  of  linie  or  of  magnesia,  or  in  what  were  then 
known  as  the  '  mild  alkalies ' ;  and  that  it  could  possess 
weight.  He  termed  carbonic  anhydride  'fixed  air.' 
Cavendish's  first  published  paper  deals  with  'Factitious 
Air';  it  appeared  in  1766,  seven  years  after  the  publica- 
tion of  Black's  memoir  on  '  Magnesia  alba,  Quick-lime,  and 
other  Alkaline  Substances.'  '  Factitious  air  '  was  defined 
by  Cavendish  as  '  any  kind  of  air  which  is  contained  in 
other  bodies  in  an  unelastic  state,  and  is  produced  from 
thence  by  art.'  He  first  treats  of  hydrogen,  next  of 
carbon  dioxide,  and  lastly  of  gases  evolved  during  fermen- 
tation and  putrefaction.  Although  not  the  first  to  prepare 
hydrogen  (for  it  must  have  been  known  for  centuries  that 
an  inflammable  gas  was  evolved  on  bringing  metals  into 
contact  with  certain  dilute  acids),  yet  he  was  the  first  to 
characterise  hydrogen  as  a  definite  substance,  and  not  a 
mere  variety  of  common  air.  He  prepared  this  gas  from 
zinc,  iron,  or  tin,  and  weak  sulphuric  or  hydrochloric  acid. 
He  found  that  the  substance  was  identical  in  each  case, 
by  weighing  a  known  volume ;  which  he  did  with  no  great 
accuracy  in  a  bladder,  but  with  considerable  exactitude 
by  weighing  a  flask  containing,  for  example,  zinc  and 
acid,  unmixed ;  and  after  mixture,  weighing  again ;  a 
further  experiment  served  to  determine  the  volume  of  gas 
obtainable  from  a  known  weight  of  zinc.  Another  method 
of  establishing  their  identity,  curious  to  our  notions,  was 
to  mix  the  sample  with  a  known  volume  of  air,  and 
estimate  the  loudness  of  the  explosion  which  took  place 
on  applying  a  flame.  Cavendish  also  prepared  '  the 
volatile  sulphurous  acid,'  by  substituting  concentrated 
sulphuric  acid  for  dilute;  and  a  non-inflammable  air 
(nitric  oxide),  by  the  action  of  nitric  acid. 

Cavendish  did  not  suppose  that  the  'air'  came  from 
the  acid,  but  from  the  metal.     It  must  be  remembered 


38    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

that  at  that  time,  the  current  doctrine  was  that  when 
substances  burn,  they  lost  a  principle,  to  which  the  name 
'  phlogiston '  had  been  applied  by  Stahl,  the  propounder  of 
the  doctrine.  The  hydrogen  evolved  was  at  first  sup- 
posed by  Cavendish  to  be  the  long-sought  phlogiston 
itself.  But  fuller  consideration  induced  him  to  change 
his  view ;  and  he  subsequently  held  that  hydrogen  was  a 
hydrate  of  phlogiston,  or  a  compound  of  that  hypothetical 
substance  with  water.  In  this  paper,  too,  as  well  as  in 
one  which  followed,  Cavendish  added  many  facts  to  those 
which  had  been  published  by  Black  on  the  properties  of 
carbonic  acid;  but  as  these  contain  little  of  theoretical 
interest,  they  need  not  detain  us. 

Seventeen  years  later,  the  next  of  his  '  pneumatic ' 
papers  was  published.  It  was  entitled,  '  An  Account  of  a 
New  Eudiometer.'  The  eudiometer,  which  in  no  way 
resembled  the  picture  of  the  instrument  usually  ascribed 
to  him,  was  designed,  not  for  the  explosion  of  a  mixture 
of  two  gases,  but  for  the  removal  of  oxygen  from  air,  by 
means  of  nitric  oxide.  With  its  aid,  he  determined  the 
composition  of  many  samples  of  air,  and  his  final  result, 
translated  into  our  method  of  statement,  gave  for  the 
proportion  of  oxygen  in  air  the  extraordinarily  accurate 
number,  20*83  per  cent. 

Cavendish's  next  paper  in  order  of  publication  (1784) 
gave  the  results  of  experiments  begun  in  1781.  Its  title 
is  '  Experiments  on  Air.'  The  object  of  these  experiments 
was  to  'find  out  the  cause  of  the  diminution  which  com- 
mon air  is  well  known  to  suffer  by  all  the  various  ways 
in  which  it  is  phlogisticated,  and  to  discover  what  becomes 
of  the  air  thus  lost  or  condensed.'  His  first  idea  was  that 
this  treatment  might  result  in  the  formation  of  '  fixed 
air.'  But  having  disproved  this,  he  proceeded  to  try 
whether,  as  some  of  Priestley's  experiments  appeared  to 
show,  '  the  dephlogisticated  part  of  common  air  might 


THE  GREAT  LONDON  CHEMISTS  39 

nob  by  phlogistication  be  changed  into  nitrous  or  vitri- 
olic acid ' ;  i.e.  whether  oxygen,  by  reduction,  might  not 
be  converted  into  nitric  or  sulphuric  acid.  Absorbing 
the  oxygen  by  burning  sulphur,  he  failed  to  find  nitric 
acid;  and  using  nitric  oxide  as  the  absorbent,  the  re- 
sulting nitrate  and  nitrite  contained  no  sulphate.  He 
therefore  tried  firing  a  mixture  of  hydrogen  and  air  by 
means  of  an  electric  spark ;  an  experiment  which  led  to 
the  discovery  of  the  composition  of  water.  Having 
burned  500,000  grain  measures  of  inflammable  air  (hydro- 
gen) with  two  and  a  half  times  its  volume  of  common 
air,  he  collected  upwards  of  135  grains  of  water, '  which 
had  no  taste  nor  smell,  and  which  left  no  sensible  sedi- 
ment when  evaporated  to  dryness.' 

It  is  impossible  in  a  short  sketch  like  the  present  to 
enter  into  a  description  of  the  exceedingly  ingenious 
experiments  devised  to  show  whence  the  acid  was  derived 
which  is  formed  when  the  hydrogen  is  present  in  insuf- 
ficient amount ;  we  must  be  content  to  remember  that  in 
default  of  hydrogen  with  which  to  combine,  some  of  the 
oxygen  unites  with  the  nitrogen,  yielding  nitrous  and 
nitric  acids. 

Although  Cavendish  employs  the  language  of  the 
phlogistic  theory  in  stating  his  conclusions,  yet  it  must 
not  be  supposed  that  he  was  ignorant  of  the  newer  views, 
propounded  by  Lavoisier.  In  the  memoir  which  we  have 
been  considering,  he  states  his  conclusions  in  the  new 
phraseology ;  but  he  concludes  as  follows :  '  It  seems, 
therefore,  from  what  has  been  said,  as  if  the  phenomena 
of  nature  might  be  explained  very  well  on  this  principle 
without  the  help  of  phlogiston;  and  indeed,  as  adding 
dephlogisticated  air  to  a  body  comes  to  the  same  thing 
as  depriving  it  of  its  phlogiston,  and  adding  water  to  it, 
and  as  there  are  perhaps  no  bodies  entirely  destitute  of 
water,  and  as  I  know  no  way  by  which  phlogiston  can  be 


40    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

transferred  from  one  body  to  another  without  leaving  it 
uncertain  whether  water  is  not  at  the  same  time  trans- 
ferred, it  will  be  very  difficult  to  determine  by  experiment 
which  of  these  opinions  is  the  truest;  but  as  the  com- 
monly received  principle  of  phlogiston  explains  all 
phenomena,  at  least  as  well  as  Mr.  Lavoisier's,  I  have 
adhered  to  that.'  We  shall  meet  with  this  same  difficulty 
again,  when  we  consider  Davy's  experiments,  which  led 
to  true  views  concerning  the  nature  of  chlorine. 

Cavendish's  aim  in  these  experiments,  stated  in  modern 
language,  was  to  find  out  what  becomes  of  the  oxygen, 
when  substances  burn  in  air ;  whether  the  production  of 
carbon  dioxide  is  a  constant  accompaniment  of  com- 
bustion. He  mentions  five  ways  in  which  air  may  be 
deprived  of  oxygen,  namely,  by  the  calcination  of  rnetals ; 
by  burning  in  it  sulphur  or  phosphorus;  by  mixing  it 
with  nitric  oxide;  by  exploding  it  with  hydrogen;  and 
lastly  by  submitting  it  to  the  action  of  electric  sparks. 
In  the  second  series  of  his  experiments  on  air,  he  ex- 
amines in  detail  the  action  of  a  continued  rain  of  sparks 
on  air ;  and  this  led  to  the  discovery  of  the  composition 
of  nitric  acid ;  for  the  '  caustic  lees '  on  evaporation  to 
dryness  '  left  a  small  quantity  of  salt,  which  was  evidently 
nitre,  as  appeared  by  the  manner  in  which  paper  im- 
pregnated with  a  solution  of  it  burned.'  But  he  doubted 
whether  '  there  are  not,  in  reality,  many  different  sub- 
stances confounded  by  us  under  the  name  of  phlogisticated 
air.'  He  '  therefore  made  an  experiment  to  determine 
whether  the  whole  of  a  given  portion  of  the  phlogisticated 
air  of  the  atmosphere  could  be  reduced  to  nitrous  acid, 
or  whether  there  was  not  a  part  of  a  different  nature 
from  the  rest,  which  would  refuse  to  undergo  that  change.' 
On  experiment,  he  found  that  '  if  there  is  any  part  of  the 
phlogisticated  air  of  our  atmosphere  which  differs  from 
the  rest,  and  cannot  be  reduced  to  nitrous  acid,  we  may 


THE  GREAT  LONDON  CHEMISTS  41 

safely  conclude  that  it  is  not  more  than  T^  part  of  the 
whole.'  Here  he  was  nearly  right;  about  one  per  cent, 
is  actually  left ;  and  it  has  been  recently  recognised  as  a 
separate  element,  and  named  Argon.  And  still  more 
recently,  the  argon  has  been  shown  to  contain  a  small 
proportion  of  other  gases,  also  elements,  to  which  the  names 
helium,  neon,  krypton  and  xenon  have  been  given.  This 
paper  was  the  last  on  chemical  subjects  published  by 
Cavendish. 

These  two  men,  Boyle  and  Cavendish,  both  rank  as 
great  men.  The  first  has  been  termed  with  justice  f  the 
father  of  modern  chemistry ' ;  the  second  by  '  weighing  the 
earth/  and  by  establishing  the  composition  of  water  and 
of  air,  has  even  more  decided  claims  to  that  title.  Each 
was  in  advance  of  his  age :  Boyle  by  reason  of  his  calm 
philosophical  spirit,  and  clear  judgment;  Cavendish  in 
the  power  he  possessed,  in  an  age  of  qualitative  en- 
deavours, of  carrying  out  quantitative  experiments  with 
the  most  refined  accuracy,  and  of  drawing  from  them 
correct  conclusions. 


II.   DAVY   AND   GRAHAM 

Between  a  prospect  over  an  extensive  landscape,  and  a 
retrospect  in  history,  an  instructive  analogy  may  be 
drawn.  It  is  true  that  when  the  spectator  is  removed 
from  the  object  by  a  great  distance,  whether  of  time  or 
space,  its  appearance  is  ill-defined  and  hazy,  as  are  to  us 
the  personalities  of  the  ancient  Egyptians,  Greeks,  and 
Arabians  ;  and  just  as  the  imagination  supplies  details  to 
the  distant  features  of  a  landscape,  details  which  may  or 
may  not  be  in  consonance  with  fact,  so  through  the  mists 
of  time  we  are  apt  to  read  into  the  writings  of  the 


42    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

ancients  ideas  which  have  their  origin  rather  in  our 
own  brains  than  in  their  works.  Objects  in  the  middle 
distance  are  perhaps  most  truthfully  interpreted.  They 
are  not  obscured  by  the  haze  of  perspective  nor  by  the 
multitudinous  aggregations  of  propinquity.  So  it  is  with 
Boyle  and  with  Cavendish.  But  with  Davy,  and  with 
Graham,  whose  lives  and  works  are  to  form  the  subject 
of  this  essay,  it  is  difficult  to  select  from  their  writings 
those  salient  features  which  will,  in  the  course  of  another 
half-century,  stand  out  clearly  and  luminously  among 
the  labours  of  their  contemporaries.  In  chemical  and 
physical  work,  as  in  life,  safety  lies  in  a  happy  mean ;  and 
it  shall  be  my  endeavour  to  avoid  unimportant  details, 
while  presenting  the  main  characteristics  of  the  work  of 
these  two  remarkable  men.  The  difficulty  is  to  know 
what  to  omit ;  for  that  which  appears  unimportant  to-day 
may  to-morrow  turn  out  to  be  essential  to  the  fundamental 
doctrines  of  our  science. 

At  the  time  when  Cavendish  was  beginning  his  splendid 
series  of  experiments  on  gases,  Humphry  Davy,  an  infant 
of  two,  was  beginning  to  show  signs  of  that  ability  which 
so  remarkably  distinguished  him  in  after  life.  At  that 
age,  he  could  speak  fluently ;  a  year  or  two  later,  he  was 
sent  to  school,  where  he  learned  to  read  and  write  before 
he  was  six ;  and  in  his  seventh  year  he  was  sent  to  the 
Grammar  School  at  Truro,  his  native  place.  Looking 
back  on  his  experiences  there,  from  the  standpoint  of  a 
young  man  of  twenty-two,  he  wrote :  '  I  consider  it  fortu- 
nate that  I  was  left  much  to  myself  when  a  child,  and 
put  upon  no  particular  plan  of  study,  and  that  I  enjoyed 
much  idleness  at  Mr.  Coryton's  school.'  Do  not  we  err 
in  insisting  too  much  on  the  systematic  employment  of 
time  by  the  boys  of  our  modern  schools  ?  For,  be  it  re- 
membered, the  compulsory  cricket  and  football,  so  com- 
mon in  our  schools,  is  to  some  boys  the  hardest  task 


THE  GREAT  LONDON  CHEMISTS  43 

they  have  to  master,  and   leaves   no   time  for   salutary 
idleness. 

Like  many  boys,  Davy  entered  the  study  of  chemistry 
through  the  doorway  of  fireworks.  His  favourite  amuse- 
ments were  fishing,  and  the  art  of  rhyming.  During  his 
whole  life,  he  never  lost  the  taste  for  these  two  pursuits ; 
and  though  it  must  be  confessed  that  he  was  a  more 
successful  fisher  than  poet,  still  his  verses  have  a  certain 
amount  of  merit,  and  betoken  a  considerable  gift  of 
imagination,  necessary  to  the  higher  achievements  in 
science,  as  he  indicates  in  the  two  stanzas  which  I  venture 
to  quote : — 

While  superstition  rules  the  vulgar  soul, 

Forbids  the  energies  of  man  to  rise, 
Raised  far  above  her  low,  her  mean  control, 

Aspiring  genius  seeks  her  native  skies. 

She  loves  the  silent,  solitary  hours ; 

She  loves  the  stillness  of  the  starry  night, 
When  o'er  the  bright'ning  view  Selene  pours 

The  soft  effulgence  of  her  pensive  light. 

In  his  later  efforts  he  preferred  decasyllabics;  and 
though  his  sentiments  thus  expressed  are  praiseworthy, 
his  execution  rarely  exceeds  the  level  demanded  from  a 
poet  laureate. 

At  the  early  age  of  fifteen,  his  school  education  was  at 
an  end.  For  the  next  year  he  continued  in  the  '  enjoy- 
ment of  much  idleness.'  But  in  the  beginning  of  the 
year  1795  he  was  apprenticed  to  Mr.  Borlase,  surgeon  and 
apothecary,  in  his  native  town.  Then  the  demon  of  work 
seized  on  him,  and  he  threw  himself  into  the  task  of  self- 
improvement  with  irresistible  ardour.  His  scheme  of 
study  is  so  remarkable,  and  so  extensive,  that  I  cannot 


44    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

resist  the  temptation  to  quote  it  at  full  length.     Here 
it  is  : — 

1 .  THEOLOGY  OR  EELIGION,  taught  by  Nature. 

ETHICS,  or  moral  virtues,  by  Revelation. 

2.  GEOGRAPHY. 

3.  MY  PROFESSION—  4.  LANGUAGE — 

1.  Botany.  1.  English. 

2.  Pharmacy.  2.  French. 

3.  Nosology.  3.  Latin. 

4.  Anatomy.  4.  Greek. 

5.  Surgery.  5.  Italian. 

6.  Chemistry.  6.  Spanish. 

5.  LOGIC.  7-  Hebrew. 

6.  PHYSICS. 

1.  The  doctrines  and  properties  of  natural  bodies. 

2.  Of  the  operations  of  nature. 

3.  Of  the  doctrines  of  fluids. 

4.  Of  the  properties  of  organised  matter. 

5.  Of  the  organisation  of  matter. 

6.  Simple  astronomy. 

7.  MECHANICS.  8.  HISTORY  AND  CHRONOLOGY. 
9.  RHETORIC  AND  ORATORY.  10.  MATHEMATICS. 

Which  of  us  has  undertaken  a  course  of  study  so  exten- 
sive, and  so  inclusive  ? 

Following  out  this  course,  not  quite  in  the  prescribed 
order,  however,  he  reached  the  subject  of  chemistry  in 
January  1798.  His  textbooks  were  Lavoisier's  Chemistry 
and  Nicholson's  Dictionary  of  Chemistry.  He  kept  up 
the  study  of  mathematics  during  the  whole  course,  having 
begun  in  1796 :  for  he  remarks  on  its  usefulness  as  a 
preliminary  to  the  study  of  chemistry  and  physics.  In 
his  self-imposed  task  of  mastering  chemistry,  he  at  once 
began  practical  work,  having  fitted  up  a  small  laboratory, 
furnished  with  the  very  simplest  and  most  inexpensive 


THE  GREAT  LONDON  CHEMISTS  45 

apparatus,  in  Mr.  Tonkins's  house.  About  four  months 
after  beginning  his  chemical  studies  he  was  in  corre- 
spondence with  Dr.  Beddoes,  a  medical  man  residing  at 
Clifton,  on  the  subject  of  heat  and  light.  This  corre- 
spondence was  fraught  with  momentous  consequences  for 
Davy;  for  it  led  to  his  being  offered  the  position  of 
superintendent  of  the  'Pneumatic  Institution,'  founded 
by  the  doctor,  with  the  help  of  Josiah  Wedgwood  and  Mr. 
Gregory  Watt,  youngest  son  of  James  Watt,  with  the 
object  of  experimenting  with  the  gases,  at  that  time 
recently  discovered,  in  order  to  ascertain  whether  they 
would  prove  suitable  as  remedial  agents. 

In  reviewing  the  career  of  a  man,  it  is  interesting  to 
note  the  motives  which  underlie  his  actions.  The  latter, 
indeed,  may  not  always  be  worthy  of  the  sentiments  which 
give  them  birth,  but  it  is  just  to  give  credit  for  pure 
intentions,  and  to  form  an  estimate  of  character  by  taking 
both  motive  and  action  into  consideration.  In  one  of  the 
earliest  of  Davy's  notebooks,  intended  for  no  eye  but  his 
own,  there  is  this  entry :  '  I  have  neither  riches,  nor 
power,  nor  birth  to  recommend  me ;  yet,  if  I  live,  I  trust 
I  shall  not  be  of  less  service  to  mankind  and  to  my 
friends  than  if  I  had  been  born  with  these  advantages.' 
And  again,  in  1821,  nearly  twenty-five  years  later,  his 
diary  contains  the  aspiration, '  May  every  year  make  me 
better — more  useful,  less  selfish,  and  more  devoted  to  the 
cause  of  humanity  and  science.'  These  are  noble  words, 
and  they  lead  one  to  form  a  high  estimate  of  the  charac- 
ter of  Humphry  Davy. 

In  January  1799  he  went  to  the  Pneumatic  Institute, 
and  worked  under  the  patronage  of  Dr.  Beddoes.  By  the 
following  year  he  had  finished  his  classical  research  on 
nitrous  oxide,  and  had  discovered  and  investigated  its 
remarkable  anaesthetic  properties.  He  also  discovered 
the  composition  of  nitric  acid,  nitric  oxide,  nitric  peroxide, 


46    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

and  ammonia.  By  1801  he  had  begun  his  experiments 
with  the  '  galvanic  battery,'  which  was  to  be  so  fruitful  of 
important  results  in  his  hands.  During  these  two  years, 
he  published  no  fewer  than  nine  papers  in  the  scientific 
journal  of  his  time,  Nicholsons  Journal,  the  predecessor 
of  the  Philosophical  Magazine, — the  result  of  astonishing 
industry. 

At  this  period  of  his  life,  Davy's  acumen  led  him  to 
avoid  undue  theorising,  and  to  endeavour  to  accumulate 
facts.  His  own  words  are :  '  When  I  consider  the  variety 
of  theories  that  may  be  formed  on  the  slender  foundation 
of  one  or  two  facts,  I  am  convinced  that  it  is  the  business 
of  the  true  philosopher  to  avoid  them  altogether.  It  is  ' 
more  laborious  to  accumulate  facts  than  to  reason  con- 
cerning them  ;  but  one  good  experiment  is  of  more  value 
than  the  ingenuity  of  a  brain  like  Newton's.'  In  the  light 
of  this  opinion,  it  is  interesting  to  examine  the  programme 
which  he  laid  down  for  himself  at  the  time.  It  was 
written  in  the  spring  of  1799,  and  is  as  follows  : — 

*  To  decompose  the  muriatic,  boracic,  and  fluoric  acids ; 
to  try  triple  affinities,  and  the  contact  with  heated  com- 
bustible bodies  at  a  high  temperature. 

'  To  ascertain  all  the  phenomena  of  oxydation. 

'  To  discover  with  accuracy  the  vegetable  process.' 

The  decomposition  of  the  muriatic  and  the  boracic 
acids  was  successfully  accomplished  at  a  much  later  date. 
But  the  '  phenomena  of  oxydation '  are  even  now  known 
only  imperfectly.  He  contributed  useful  facts,  however, 
as  we  shall  see,  to  our  knowledge  of  '  the  vegetable 
process.' 

Consistently  with  these  ideas  regarding  the  relative 
merits  of  theory  and  practice,  Davy  made  his  greatest 
successes  in  the  realm  of  facts.  Where  he  attempts 
theorising,  the  results  are  not  happy.  It  is  true  that  he 
did  not  risk  the  publication  of  his  theories ;  but  those 


THE  GREAT  LONDON  CHEMISTS  47 

revealed  by  his  notebooks  have  not  much  to  recommend 
them.  He  allowed  his  imagination,  of  which  he  possessed 
a  rich  share,  full  scope  in  other  directions.  Many  of  his 
imaginative  projects  were,  however,  not  realised.  Among 
them  may  be  mentioned  an  epic  poem,  in  six  books, 
entitled  The  Epic  of  Moses,  written,  what  there  is  of  it,  in 
decasyllabics.  He  possessed  a  deeply  religious  nature; 
and  he  regarded  '  this  little  earth  as  but  the  point  from 
which  we  start  towards  a  perfection  bounded  only  by 
infinity.' 

In  1801  Davy  was  recommended  by  Professor  Hope  of 
Edinburgh  for  the  lectureship  at  the  Royal  Institution, 
which  had  been  founded  a  few  years  previously  by  Count 
Rurnford,  on  the  resignation  of  Dr.  Garnet,  the  first 
Professor  of  Chemistry  there.  He  delivered  his  first 
lecture  in  April  1801,  and  he  at  once  achieved  a  great 
success.  To  quote  from  an  account  by  a  contemporary 
witness :  '  The  sensation  created  by  his  first  course  of 
lectures  at  the  institution,  and  the  enthusiastic  admira- 
tion which  they  obtained,  is  at  this  period  hardly  to  be 
imagined.  Men  of  the  first  rank  and  talent — the  literary 
and  the  scientific,  the  practical  and  the  theoretical — blue- 
stockings and  women  of  fashion,  the  old  and  the  young,  all 
crowded,  eagerly  crowded,  the  lecture-room.  His  youth,  his 
simplicity,  his  natural  eloquence,  his  chemical  knowledge, 
his  happy  illustrations  and  well-conducted  experiments,  ex- 
cited universal  attention  and  unbounded  applause.  Com- 
pliments, invitations,  and  presents  were  showered  on  him  in 
abundance  from  all  quarters ;  his  society  was  courted  by 
all,  and  all  appeared  proud  of  his  acquaintance.'  With 
all  these  temptations  to  neglect  his  work,  he  remained 
faithful  to  his  charge.  In  1803  he  wrote  :  '  My  real,  my 
waking  existence  is  among  the  objects  of  scientific 
research.  Common  amusements  and  enjoyments  are 
necessary  to  me  only  as  dreams  to  interrupt  the  flow  of 


48    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

thoughts  too  nearly  analogous  to  enlighten  and  vivify.' 
Still  many  of  our  scientific  workers  of  to-day  would  be 
glad  if  they  could  extract  as  much  leisure  time  from 
amidst  their  daily  employments.  Davy  generally  entered 
the  laboratory  about  ten  or  eleven  o'clock,  and  if  uninter- 
rupted, remained  there  till  about  three  or  four.  His 
evenings  were  almost  invariably  spent  in  dining  out,  and  at 
evening  parties  afterwards.  '  To  the  frequenters  of  these 
parties  he  must  have  appeared  a  votary  of  fashion,  rather 
than  of  science,'  as  his  brother  remarked. 

Yet,  during  the  years  which  followed,  he  accomplished 
an  immense  amount  of  very  remarkable  work.  Besides 
investigating,  by  the  request  of  the  managers  of  the  Royal 
Institution,  the  chemistry  of  tanning,  an  investigation 
which  led  to  the  use  of  catechu  as  a  substitute  for  the 
old-fashioned  oak-bark,  he  lectured,  by  the  request  of  the 
Board  of  Agriculture,  on  '  The  Connection  of  Chemistry 
with  Vegetable  Physiology.'  These  lectures  were  given 
every  year,  and  in  them  were  incorporated  the  results  of  a 
considerable  number  of  experiments  made  by  him,  or 
under  his  direction,  on  the  chemistry  of  plants.  In  1813, 
when  he  ceased  to  lecture  on  the  subject,  he  published  his 
lectures,  under  the  title  The  Elements  of  Agricultural 
Chemistry.  For  the  copyright  of  this  work  he  received 
one  thousand  guineas,  and  fifty  guineas  for  each  subse- 
quent edition.  Truly  he  was  a  fortunate  man  ! 

Between  January  1801  and  April  1812  he  accomplished 
two  of  his  most  remarkable  pieces  of  work ;  first,  on  the 
decomposition  of  the  alkalies ;  and  second,  on  the  nature 
of  chlorine.  As  his  name  rives  chiefly  in  connection  with 
these  two  investigations,  and  in  his  research  on  the 
nature  of  flame,  which  culminated  in  the  invention  of  the 
safety-lamp,  I  shall  give  some  account  of  them  in 
minuter  detail. 

The  Swedish  chemist,  Scheele,  had  discovered  in  1774, 


THE  GREAT  LONDON  CHEMISTS  49 

that  on  treating  manganese  dioxide  with  hydrochloric 
acid,  or  as  it  was  then  called  '  spiritus  salis/  in  a  flask  to 
which  a  bladder  had  been  attached,  a  '  yellow  air '  filled 
the  bladder,  which  possessed  a  suffocating  smell,  which 
bleached  litmus  paper  and  flowers,  and  which  attacked 
metals,  even  gold.  He  named  this  new  gas  '  dephlogisti- 
cated  marine  acid/  imagining  that  the  manganese  had 
deprived  the  marine  acid  of  its  '  phlogiston,'  and  that  it 
had  consequently  been  converted  into  the  yellow  gas. 
Count  Berthollet,  in  1788,  prepared  this  gas,  and  on 
saturating  with  it  water  cooled  with  ice,  he  discovered 
that  a  solid  crystalline  hydrate  separated  from  the  water. 
Having  exposed  a  solution,  thus  obtained,  to  sunlight,  he 
noticed  the  evolution  of  oxygen,  and  he,  therefore,  con- 
cluded that  the  dephlogisticated  marine  acid  was  in 
reality  a  compound  of  marine  acid  with  oxygen,  since, 
under  the  action  of  sunlight,  oxygen  was  evolved,  and 
marine  acid  left.  This  idea,  according  to  Berthollet, 
readily  explained  the  action  of  the  solution  of  the  yellow 
gas  on  metals;  for  it  might  be  supposed  to  give  up  to 
metals  its  oxygen,  and  the  metallic  oxide  would  then,  as 
usual,  dissolve  in  the  marine  acid.  In  consequence  of 
this  observation,  M.  de  Morveau,  in  conjunction  with 
Lavoisier,  Berthollet,  and  de  Fourcroy,  in  drawing  up 
their  Meihode  de  nomenclature  chimique,  proposed  for 
the  gas  the  name  'Oxymuriatic  acid.'  To  follow  the 
further  history  of  chlorine,  it  will  be  advisable  to  pause, 
and  consider  Davy's  researches  on  the^alkali  metals. 

Before  leaving  Bristol,  Davy  had*  begun  experiments 
with  the  galvanic  battery.  On  reaching  London,  he  con- 
tinued his  electrical  work;  and  in  1807  he  published  a 
remarkable  paper  on  the  'Chemical  Agencies  of  Elec- 
tricity.' It  had  been  shown  that  when  the  two  poles  of  a 
battery  with  platinum  terminals  were  plunged  into  two 
vessels  of  water,  connected  together  by  wet  asbestos,  or 

D 


50    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

cotton  wick,  an  acid  appeared  round  the  positive  wire,  and 
an  alkali  round  the  negative  wire.  Davy  showed  by  a 
series  of  convincing  experiments  that  the  alkali  is  usually 
potash  or  soda  derived  from  the  glass,  and  the  acid 
usually  hydrochloric  acid  from  the  common  salt  present 
as  an  impurity  in  the  water.  From  experiments  such  as 
these  he  evolved  a  theory  that  all  substances  which  have 
a  chemical  affinity  for  each  other  are  in  opposite  states  of 
electrification,  and  that  the  positive  pole  attracts  those 
constituents  of  the  solution  which  possess  a  negative 
charge,  while  the  negative  pole  attracts  the  positively 
charged  component.  The  more  powerful  the  battery, 
the  greater  the  force  of  these  attractions  and  repulsions. 
For  example,  oxygen  and  acids  are  negative  bodies,  for 
they  are  attracted  by  the  positive  pole,  and  liberated 
there;  whereas  metals  and  their  oxides,  and  hydrogen, 
nitrogen,  carbon,  and  selenium  are  positive,  because  they 
separate  at  the  negative  pole.  It  ought,  therefore,  to  be 
possible,  by  help  of  a  sufficiently  strong  electric  current, 
to  decompose  any  compound  whatsoever.  Davy  carried 
his  inference  farther,  and  suggested  that  the  reason  of 
chemical  attraction  is  the  oppositely  charged  state  of  the 
components  of  a  compound.  A  compound  is  an  elec- 
trically neutral  body,  for  the  constituents  of  the  com- 
pound, in  uniting,  have  respectively  equal  and  opposite 
charges,  which  neutralise  each  other  by  the  act  of  com- 
bination. But  a  current  of  electricity,  passing  through 
such  a  compound,  might  neutralise  the  electricity  in  each, 
and  so,  by  overcoming  their  attractions,  decompose  the 
compound. 

By  applying  these  ideas,  he  succeeded  in  decomposing 
the  '  fixed  alkalies,'  as  caustic  soda  and  potash  used  to  be 
called,  into  oxygen,  hydrogen,  and  the  metals  sodium  and 
potassium.  Having  failed  to  obtain  any  products  from 
aqueous  solutions  of  these  compounds,  except  oxygen  and 


THE  GREAT  LONDON  CHEMISTS  51 

hydrogen,  he  next  attempted  to  pass  a  very  powerful 
current  through  the  fused  alkalies.  Potash  was  fused  in 
a  platinum  spoon,  connected  with  the  positive  side  of  a 
battery ;  and  a  platinum  wire,  connected  with  the  negative 
pole  of  the  battery,  was  dipped  into  the  fused  alkali.  The 
result  was  an  intense  light  at  the  negative  wire,  and  a 
column  of  flame  from  the  point  of  contact.  On  reversing 
the  current,  'aeriform  globules,  which  inflamed  in  the 
atmosphere,  rose  through  the  potash.'  The  substance 
produced  was  evidently  inflammable,  and  was  destroyed 
at  the  moment  of  liberation.  Better  results  were  obtained 
by  the  use  of  slightly  moist  potash ;  and  small  metallic 
globules  were  collected, '  precisely  similar  in  visible  char- 
acteristics to  quicksilver.'  c  These  globules  numerous  ex- 
periments soon  showed  to  be  the  substance  I  was  in  search 
of,  and  a  peculiar  inflammable  substance,  the  basis  of 
potash.'  Soda  gave  an  analogous  result;  and  thus  the 
metals  of  the  alkalies  were  discovered. 

These  new  metals  burned  in  oxygen,  forming  the 
alkalies  from  which  they  had  been  obtained ;  they  also 
burned  in '  oxymuriatic  acid/  forming  '  muriates '  of  potash 
or  soda.  They  decompose  water  with  evolution  of  hydro- 
gen, giving  solutions  of  the  respective  alkalies ;  and  they 
form  compounds  with  sulphur  and  with  phosphorus. 
They  reduce  metals  such  as  copper,  iron,  lead,  and  tin 
from  their  oxides ;  and  they  attack  glass,  apparently 
liberating  the  '  basis  of  the  silex.' 

Fairly  accurate  estimations  were  made  of  the  proportion 
of  these  new  metals  in  the  alkalies,  which  were  believed 
by  Davy  to  be  oxides ;  and  thus  the  approximate  composi- 
tion of  these  compounds,  which  at  one  time  were  believed 
to  be  elements,  was  definitely  established. 

Although  similar  phenomena  were  seen  with  the  alka- 
line earths  'barytes'  and  '  strontites,'  it  was  not  found 
possible  to  isolate  the  metals ;  but  on  electrolysing  with  a 


52    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

negative  pole  of  mercury,  amalgams  were  obtained,  con- 
taining the  new  metals  barium  and  strontium ;  while 
from  lime  and  magnesia,  evidence  was  similarly  obtained 
that  they  consisted  of  metals,  named  by  Davy  calcium 
and  'magnium.'  On  removing  the  mercury  by  distilla- 
tion, white  metallic  residues  were  obtained,  still  containing 
mercury,  but  oxidising  rapidly  in  the  air,  to  the  respective 
oxides.  An  account  of  these  results  was  published  in 
1807  and  1808,  in  the  Philosophical  Transactions. 

In  December  1808,  the  celebrated  paper  on  the  elemen- 
tary nature  of  chlorine  was  read.  Having  failed  to  obtain 
any  other  products  than  hydrogen  and  oxygen  on  passing 
a  current  through  an  aqueous  solution  of  muriatic  acid 
gas  in  water  (why,  is  not  so  apparent,  unless  only  dilute 
solutions  had  been  employed),  Davy  treated  dry  muriatic 
acid  gas  with  potassium.  The  gas  was  absorbed,  yielding 
-£%  of  its  volume  of  hydrogen.  He  concluded  from  this 
that  dry  muriatic  acid  gas  contained  at  least  one-third 
of  its  weight  of  water,  and  that  it  had  not  been  '  decom- 
pounded '  by  the  potassium.  His  first  attempt,  therefore, 
was  directed  to  obtaining  really  dry  muriatic  gas.  For 
this  object,  he  heated  dry  muriate  of  lime  with  dry  sul- 
phate of  iron,  with  phosphoric  glass,  and  with  dry  boracic 
acid ;  but  without  any  evolution  of  gas,  although  when 
water  was  added  to  the  ignited  mass,  quantities  of 
muriatic  gas  were  liberated.  After  numerous  attempts  of 
the  same  kind,  during  which  the  chlorides  of  sulphur  and 
phosphorus  were  discovered,  these  substances  were  them- 
selves submitted  to  the  action  of  potassium,  but  without 
the  formation  of  any  gaseous  product. 

In  an  appendix  to  these  observations,  which  were  pub- 
lished as  the  Bakerian  Lecture,  Davy  announces  the  view 
that  'muriatic  acid  gas  is  a  compound  of  a  substance, 
which  as  yet  has  never  been  procured  in  an  uncombined 
state,  and  from  one-third  to  one-fourth  of  water,  and  that 


THE  GREAT  LONDON  CHEMISTS  53 

oxymuriatic  acid  is  composed  of  the  same  substance  (free 
from  water),  united  to  oxygen.'  His  idea  then  was  that 
'  when  bodies  are  oxidated  in  muriatic  acid  gas,  it  is  by  a 
decomposition  of  the  water  contained  in  that  substance, 
and  when  they  are  oxidated  in  oxymuriatic  acid,  it  is  by 
combination  with  the  oxygen  in  that  body.'  Davy  believed 
that  the  chlorides  all  contained  oxygen. 

In  a  later  paper,  read  in  November  1809,  he  arrived  at 
the  true  explanation  of  these  facts.  It  was  based  on 
experiments  on  the  ignition  of  charcoal  to  whiteness  in 
muriatic  and  oxymuriatic  gases.  No  action  occurred ; 
and  Davy  began  to  doubt  whether,  as  universally  sup- 
posed, these  bodies  contain  any  oxygen.  He  therefore 
tried  whether  compounds  produced  by  the  action  of  oxy- 
muriatic acid  on  tin,  phosphorus,  and  sulphur  would  give 
with  ammonia  precipitates  of  the  oxides  of  these  elements, 
or  any  compounds  containing  oxygen;  and  his  experi- 
ments were  attended  with  negative  results.  He  next  con- 
sidered one  argument  that  the  so-called  '  oxymuriatic  acid ' 
contained  oxygen,  viz.  the  fact  that  on  treatment  with 
rnetals,  hydrogen  is  evolved ;  and  in  a  further  paper,  read 
in  November  1810,  he  proved  that  on  heating  barium  or 
strontium  in  the  gas,  one  volume  of  oxygen  is  liberated 
for  every  two  volumes  of  oxymuriatic  acid  absorbed.  This 
is  exactly  the  amount  of  oxygen  contained  in  the  oxide ; 
and  experiments  with  other  oxides  of  metals  resulted  in 
similar  liberation  of  all  the  oxygen  previously  combined 
with  the  metal.  From  ttfese  facts,  Davy  concluded  that 
'  to  call  a  body  which  is  not  known  to  contain  oxygen,  and 
which  cannot  contain  muriatic  acid,  oxymuriatic  acid,  is 
contrary  to  the  principles  of  that  nomenclature  in  which 
it  is  adopted ' ;  and  he  therefore  proposed  for  the  gas  the 
name  chlorine. 

Many  derivatives  of  chlorine  were  made  by  Davy  for 
the  first  time ;  among  them  were  the  oxygen  compounds 


54    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

of  chlorine.  But  he  did  not  commit  himself  to  the  dog- 
matic assertion  that  this  gas  is  an  element;  on  the  con- 
trary, he  writes :  '  In  the  views  that  I  have  ventured  to 
develop,  neither  oxygen,  chlorine,  nor  fluorine  are  asserted 
to  be  elements ;  it  is  only  asserted  that,  as  yet,  they  have 
not  been  decomposed.'  It  would  be  well,  were  all  chemists 
to  imitate  Davy's  caution. 

These  views  were  combated  by  Gay-Lussac  and  The- 
nard;  but  it  would  take  too  much  time  to  follow  the 
contest.  Suffice  it  to  say,  that  Davy  came  off  with  flying 
colours. 

During  all  these  years,  honours  were  being  showered  on 
Davy.  In  1803,  he  was  made  a  Fellow  of  the  Royal 
Society ;  in  1807,  he  was  chosen  for  its  secretary,  an  office 
which  he  held  until  1812 ;  and  in  the  latter  year  he  was 
knighted.  In  his  private  diary,  in  which  he  transcribed 
his  inmost  thoughts,  there  is  a  pleasant  little  sentence, 
recording  sentiments  on  the  subject  of  honours:  '  A  man 
should  be  proud  of  honours,  not  vain  of  them.'  But 
besides  honours,  wealth  was  also  his  portion ;  for  two 
courses  of  lectures  in  Dublin,  he  was  paid  no  less  a  sum 
than  £11 70! 

In  1812,  his  Elements  of  Chemistry  was  published.  It 
was  dedicated  to  his  wife;  for  in  that  year  he  married 
Mrs.  Apreece. 

In  the  same  year,  he  nearly  lost  his  sight  by  experi- 
menting with  chloride  of  nitrogen,  which  had  recently 
deprived  its  discoverer,  Dulong,  of  a  finger.  In  1813,  he 
established  the  true  nature  of  fluorine,  and  demonstrated 
its  analogy  with  chlorine;  and  towards  the  end  of  the 
same  year,  he  paid  a  visit  to  Paris,  conveying  with  him  a 
portable  laboratory,  by  help  of  which  he  proved  the  simi- 
larity of  iodine  to  chlorine.  That  element,  which  had 
been  discovered  about  two  years  previously  by  Courtois, 
was  supposed  by  Gay-Lussac  to  yield  an  acid  identical 


THE  GREAT  LONDON  CHEMISTS  55 

with  hydrochloric  acid.  Davy  communicated  his  dis- 
covery to  Gay-Lussac,  who  by  no  means  agreed  with  his 
conclusions;  and  it  was  not  until  a  considerable  time 
had  elapsed,  and  the  latter  chemist  had  carried  out  his 
masterly  researches  on  iodine  and  its  compounds,  that  he 
became  convinced  of  the  correctness  of  Davy's  views. 

On  his  return  from  this  Continental  tour,  he  devoted 
his  time  to  the  investigation  of  the  nature  of  flame,  with 
the  result  that  he  discovered  how  to  prevent  flame  from 
spreading  into  the  adjoining  atmosphere,  by  surrounding 
it  with  a  sheath  of  wire-gauze ;  the  conducting  power  of 
the  gauze  so  cooling  the  explosive  mixture  of  gases,  that 
they  no  longer  inflame  after  traversing  the  gauze  dia- 
phragm. This  invention  was  hailed  with  the  greatest 
satisfaction  by  the  public,  as  well  as  by  those  whose 
interest  was  bound  up  in  mines;  and  in  1817,  he  was  pre- 
sented with  a  service  of  plate,  valued  at  £2500,  by  the 
owners  of  many  important  collieries.  His  services  to 
humanity  were,  indeed,  valued  so  highly,  that  in  the 
following  year  a  baronetcy  was  bestowed  on  him.  And  in 
1820,  on  the  death  of  Sir  Joseph  Banks,  who  had  presided 
over  the  meetings  of  the  Royal  Society  for  no  less  than 
forty- one  years,  Sir  Humphry  Davy  received  the  highest 
honour  which  can  be  bestowed  on  a  scientific  man,  in 
being  elected  his  successor.  He  resigned  the  presidency 
in  1827.  His  own  view  regarding  honours  was  :  '  It  is  not 
that  honours  are  worth  having,  but  it  is  painful  not  to 
have  them ' ;  and  again, '  It  is  better  to  deserve  honours 
and  not  to  have  them,  than  to  have  them  and  not  deserve 
them.'  These  sentiments  remind  one  of  Burns's  rhyming 
grace  before  meat : 

Some  hae  meat,  and  canna  eat, 

And  some  wad  eat  that  want  it ; 
But  we  hae  meat,  and  we  can  eat, 

And  sae  the  Lord  be  thankit. 


56    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

During  these  years,  Davy  published  many  papers,  having 
relation  to  the  preservation  of  metals  by  electro-chemical 
means,  with  special  reference  to  the  preservation  of  the 
copper  sheathing  of  ships.  In  1826,  these,  and  other 
similar  inquiries,  were  summed  up  in  the  '  Bakerian ' 
Lecture,  on  the  Relation  of  Electrical  and  Chemical 
Changes. 

His  scientific  work,  however,  was  nearly  at  an  end ;  for 
in  1826  he  had  a  slight  shock  of  paralysis,  and  though  he 
lived  until  1829,  it  was  in  a  continual  search  for  health. 
He  travelled  much  on  the  Continent,  and  made  partial 
recoveries ;  but  he  was  seized  by  a  final  stroke  at  Geneva 
in  May  1829,  where  he  died,  in  his  fifty-first  year. 

Sir  Humphry  Davy's  work  is  well  summed  up  in  a 
notice  published  in  Silliman's  American  Journal  of 
Science  and  Arts:  'To  conclude,  we  look  upon  Sir 
Humphry  Davy  as  having  afforded  a  striking  example  of 
what  the  Romans  called  a  man  of  good  fortune ; — whose 
success,  even  in  their  view,  was  not  however  the  result  of 
accident,  but  of  ingenuity  and  wisdom  to  devise  plans, 
and  of  skill  and  industry  to  bring  them  to  a  successful 
issue.  He  was  fortunate  in  his  theories,  fortunate  in  his 
discoveries,  and  fortunate  in  living  in  an  age  sufficiently 
enlightened  to  appreciate  his  merits/  But  let  him  speak 
his  own  epitaph;  it  is:  'My  sole  object  has  been  to  serve 
the  cause  of  humanity;  and  if  I  have  succeeded,  I  am 
amply  rewarded  in  the  gratifying  reflection  of  having 
done  so.' 

Fortunately  for  your  patience,  my  task  to-day  is  limited 
to  sketching  the  lives  of  those  chemists  who  have  gone 
from  among  us.  And  confining  myself  to  the  names  of 
those  who  must  pass  without  cavil  as  'great/  that  of 
Graham  presents  itself.  There  have  been  men  of  con- 
siderable ability,  who  have  in  their  day  done  good  and 


THE  GREAT  LONDON  CHEMISTS  57 

useful  work ;  such  men  as  Turner,  Graham's  predecessor ; 
Daniel,  who  gave  us  the  battery  known  by  his  name; 
Miller,  to  whose  painstaking  labours  we  owe  the  revision 
of  our  standards  of  weight  and  measure ;  and  many  others 
of  less  eminence.  But  of  these  I  can  only  mention  the 
names. 

The  city  of  Glasgow  gave  Graham  to  London ;  Boyle 
was  an  Irishman;  Cavendish  was  born  in  France;  and 
Davy  came  from  Cornwall.  But  London  made  some 
return  for  depriving  Glasgow  of  Graham ;  for  Penny  was 
a  Londoner,  who  passed  the  major  part  of  his  life  in 
Glasgow,  having  been  called  thither  as  successor  to 
Graham.  He,  too,  did  good  work  in  his  day;  he  was 
an  extremely  attractive  lecturer,  and  may  be  said  to  have 
brought  the  art  of  giving  professional  evidence  to  perfec- 
tion. In  the  eyes  of  many,  this  last  may  prove  no  recom- 
mendation; but  if  it  be  regarded  as  unworthy  of  the 
character  of  a  true  man  of  science,  voluntarily  to  abandon 
that  most  precious  heritage  of  a  genuine  philosopher,  an 
open  mind,  Penny  atoned  for  his  sins  by  many  beautiful 
investigations,  the  most  important  of  which  are  perhaps 
his  determinations  of  atomic  weights,  determinations 
which  even  to-day  rank  among  the  most  reliable. 

Thomas  Graham  was  the  son  of  a  Glasgow  manu- 
facturer, and  was  born  towards  the  end  of  the  year  1805. 
He  was  educated  in  the  Glasgow  High  School,  and  after- 
wards at  the  university  there.  His  university  career  lasted 
an  unusually  long  time ;  for  entering  when  he  was  four- 
teen years  of  age,  he  did  not  graduate  until  he  had  reached 
the  mature  age  of  twenty-one.  I  am  well  aware  that  to  an 
Oxford  or  Cambridge  '  man,'  the  age  of  fourteen  appears  a 
ridiculously  early  one  at  which  to  enter  the  university; 
but  in  many  cases,  as  for  instance  in  that  of  a  late 
president  of  the  Royal  Society,  Lord  Kelvin,  it  is  amply 
justified  in  its  results.  There  are  many  boys  who 


58    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

develop  early,  and  whom  it  is  unfair  to  measure  by  the 
uniform  standard  of  a  public  school. 

Graham's  teacher  of  chemistry  was  Dr.  Thomas 
Thomson,  a  man  of  European  reputation.  It  was  in  his 
textbook  of  chemistry  that  Dalton's  atomic  theory  was 
published,  before  its  author  had  committed  his  own  ideas 
to  the  press ;  and  he  was  a  man  who  maintained  the 
liveliest  interest  in  his  science,  and  whose  teaching  was 
most  stimulating.  His  teacher  of  physics,  Professor 
Meikleham,  was  also,  I  have  heard,  an  attractive  lecturer ; 
and  during  his  student  career,  Graham  devoted  much 
attention  to  physics  and  to  mathematics.  At  the  end 
of  his  student  career,  however,  Graham  had  an  unfortu- 
nate difference  of  opinion  with  his  father,  who  had 
designed  him  for  the  Church ;  with  that  reserve  which  is 
frequently  a  characteristic  of  the  Scottish  nature,  neither 
had  made  the  other  aware  of  his  wishes  in  the  choice  of 
a  profession ;  and  having  made  the  discovery,  with  that 
'dourness,'  also  characteristic  of  the  race,  neither  would 
yield  up  his  will  to  the  other.  Graham  therefore  left  his 
native  city,  and  pursued  his  studies  in  Edinburgh,  kept 
from  want .  by  the  self-sacrifice  of  his  mother  and  his 
sister  Margaret,  for  his  father  had  cut  off  supplies. 
There  he  studied  with  Dr.  Hope,  the  discoverer  of  stron- 
tium, working  diligently  the  while  at  mathematics  and 
physics,  and  so  preparing  himself  for  his  life-work.  Before 
his  student  days  were  over,  however,  he  had  begun  to 
earn  a  little  money ;  and  it  is  recorded  that  the  first  six 
guineas  which  he  earned  were  spent  in  presents  for  his 
mother  and  sister. 

Having  returned  to  Glasgow,  and  started  a  small  private 
laboratory,  it  was  not  long  before  he  was  asked  to  become 
lecturer  in  the  Mechanics'  Institute,  taking  the  place  of 
Dr.  Clark,  the  inventor  of  the  process  for  softening  water, 
who  had  been  appointed  to  the  Chair  of  Chemistry  at 


THE  GREAT  LONDON  CHEMISTS  59 

Aberdeen.  And  in  1830,  he  succeeded  Ure,  the  author 
of  the  Dictionary  of  Chemistry,  as  professor  in  'The 
Andersonian  University/  an  institution  which  had  been 
founded  in  rivalry  to  the  University  of  Glasgow,  towards 
the  end  of  the  eighteenth  century. 

In  1837,  Edward  Turner,  the  Professor  of  Chemistry 
at  the  then  newly  founded  University  of  London,  now 
University  College,  died ;  and  Graham  was  chosen  from 
among  many  candidates  as  his  successor.  He  was  much 
elated  at  the  change,  and  in  a  letter  to  my  grandmother 
(for  he  was  an  intimate  friend  of  the  family),  he  tells 
her  that  he  has  suddenly  risen  to  affluence,  being  in 
receipt  of  the  fees  of  no  fewer  than  400  students  who 
attended  his  lectures ! 

Graham  was  neither  a  fluent  nor  an  elegant  lecturer ; 
but  his  accuracy,  his  conscientiousness,  the  philosophical 
method  in  which  he  treated  his  subject,  and  his  en- 
thusiasm for  his  science  are  said  to  have  proved  very 
attractive  to  his  audience,  and  without  doubt  contributed 
to  fill  his  classroom.  The  same  characteristics  are  to  be 
noted  in  his  textbook,  which  I  venture  to  think  is  the 
best  textbook  on  chemistry  ever  written,  although  it  is 
now  completely  out  of  date.  No  longer  republished  in 
English,  it  still  survives  in  Germany,  under  the  name 
of '  Graham-Otto.' 

Until  1854,  Graham  retained  his  Chair  at  University 
College ;  but  in  that  year,  Sir  John  Herschel  resigned  his 
office  as  Master  of  the  Mint,  and  Graham  was  chosen  to 
occupy  that  position,  held  by  so  many  men  of  eminence, 
foremost  among  whom  was  Sir  Isaac  Newton.  During 
his  tenure  of  the  office,  Graham's  conscientiousness  proved 
a  sore  thorn  in  the  side  of  the  minor  officials ;  and  he  had 
a  hard  struggle  to  introduce  necessary  reforms.  His 
strength  of  character,  however,  stood  him  in  good  stead ; 
and  after  some  years  of  active  combat,  he  left  the  field 


60    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

victorious,  with  leisure  to  resume  the  scientific  work 
which  the  state  of  warfare  had  interrupted.  In  this 
office  he  remained  until  his  death,  which  took  place  in 
1869. 

Unlike  Davy,  Graham  was  of  a  modest  and  retiring 
disposition.  His  gentleness  endeared  him  to  all  those 
whom  he  admitted  within  the  circle  of  his  friends ;  and 
his  calm  judgment  rendered  him  an  invaluable  counsellor. 
Yet  he  received  his  full  meed  of  honour ;  he  was  the  first 
president  of  the  Chemical  Society ;  a  Fellow  of  the  Royal 
Society;  the  'Keith'  Medallist  of  the  Royal  Society  of 
Edinburgh;  he  twice  received  a  Royal  Medal  of  the 
Royal  Society  of  London,  and  in  1862  the  Copley  Medal, 
given  as  the  reward  of  a  life  successfully  devoted  to 
scientific  discovery ;  he  was  a  Corresponding  Member  of 
the  Institute  of  France;  and  he  received  from  that 
august  body  the  Prix  JecJcer. 

Graham's  scientific  work  admits  of  division  into  two 
groups,  one  relating  to  the  physical  behaviour  of  gases 
and  liquids,  and  the  other  to  the  constitution  of  salts. 
Besides  papers  on  these  subjects,  he  published  a  number 
of  miscellaneous  papers. 

In  the  second  of  these  groups,  his  earliest  communica- 
tion was  on  the  existence  of  compounds  containing 
alcohol  of  crystallisation,  analogous  to  the  well-known 
water  of  crystallisation.  The  analogy  between  water  and 
alcohol  was  thus  shown ;  an  analogy  which,  in  the  hands 
of  his  successor  Williamson,  played  an  important  part  in 
the  development  of  modern  views  on  the  constitution  of 
the  carbon  compounds,  and  indirectly  on  the  whole  of 
chemistry.  In  1833,  Graham  published  his  remarkable 
memoir  on  the  phosphoric  acids,  in  which  he  argued  that 
as  alcohol  could  replace  water  in  hydrated  salts,  so  water 
could  replace  bases,  in  such  salts  as  the  phosphates. 
The  acids  of  phosphorus  had  previously  been  a  puzzle  to 


THE  GREAT  LONDON  CHEMISTS  61 

chemists.  Graham  proved  that  orthophosphoric  acid 
consists  of  a  compound  of  the  anhydride,  P205,  with 
three  molecules  of  water,  and  that  each  molecule  is 
capable  of  replacement  by  the  oxide  of  such  a  metal  as 
sodium ;  that  pyrophosphoric  acid  may  be  regarded  as 
composed  of  a  molecule  of  anhydrous  phosphoric  acid 
with  two  molecules  of  water,  each  of  which  is  replaceable 
by  an  oxide;  and  that  metaphosphoric  acid  is  to  be 
represented  as  a  compound  of  one  molecule  of  anhydride 
with  one  molecule  of  .water.  The  general  term,  which 
came  to  be  used  for  this  behaviour  of  acids  was  basicity, 
and  an  acid  was  termed  monobasic,  dibasic,  or  tribasic, 
according  as  it  was  capable  of  uniting  with  one,  two,  or 
three  molecules  of  base;  yet  it  might  contain  the  same 
anhydrous  oxide  in  each  case.  These  views  of  Graham's 
made  it  possible  to  account  for  the  fact,  at  that  time  most 
mysterious,  that  on  mixing  nitrate  of  silver,  with  its 
neutral  reaction,  with  alkaline  phosphate  of  sodium,  an 
acid  liquid  was  the  result.  These  experiments  of  Graham's 
paved  the  way  for  the  later  theory,  that  acids  are  salts  of 
hydrogen.  In  Graham's  language,  the  three  phosphoric 
acids  were '  terphosphate,  biphosphate,  and  phosphate  of 
water ' ;  for  he  understood  by  the  term  '  phosphoric  acid ' 
what  we  nowadays  name  phosphoric  anhydride.  The  word 
phosphate,  however,  is  now  applied  to  the  group  P04, 
and  hence  the  name  phosphates  of  hydrogen.  Graham 
was  the  first  to  recognise  that  (to  quote  his  own  words) 
'  when  one  of  these  compounds  (the  phosphoric  acids) 
is  treated  with  a  strong  base,  the  whole  or  a  part  of  the 
water  is  supplanted,  but  the  amount  of  base  in  combina- 
tion with  the  acid  remains  unaltered!  We  should  now 
say, '  the  whole  or  a  part  of  the  hydrogen  of  the  acid  is 
supplanted,  but  the  total  number  of  atoms  of  hydrogen 
plus  metal  in  the  salt  remains'unaltered.' 

Continuing  the  train  of  ideas  aroused  by  his  researches 


62    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

on  the  phosphoric  acids,  Graham  next  advanced  the  sug- 
gestion that  certain  salts  may  be  substituted,  molecule  for 
molecule,  for  water  of  crystallisation.  Thus,  sulphate  of 
zinc  ordinarily  crystallises  with  seven  molecules  of  water, 
forming  the  heptahydrate,  ZnS04.7H20.  It  is  possible  to 
replace  one  of  these  molecules  of  water  with  a  mole- 
cule of  potassium  sulphate,  obtaining  the  double  salt, 
ZnS04.K2S04.6H20.  It  appeared,  too,  with  this  and 
similar  salts,  that  six  molecules  of  water  may  be  expelled 
at  a  lower  temperature  than  the  seventh,  which  may  be 
supposed  to  be  the  one  which  is  replaced  by  the  potassium 
sulphate  in  the  double  salt. 

Experiments  were  also  made  on  the  heat  evolved  on 
neutralising  bases  with  acids,  and  on  the  solution  of  salts 
in  water.  Such  experiments  on  salt  were  carried  on  until 
1843. 

But  Graham  had  all  the  while  another  set  of  re- 
searches in  progress,  in  which  he  attempted  to  arrive 
at  some  definite  knowledge  regarding  the  constitution  of 
matter.  Recognising  that  the  gaseous  state  represents 
matter  in  a  simpler  condition  than  that  of  liquid  or  solid, 
his  experiments  were  largely  directed  towards  elucidating 
the  properties  of  gases.  These  experiments  were  started 
in  1836.  From  an  observation  of  Doebereiner's,  that  in  a 
cracked  cylinder,  containing  hydrogen,  and  standing  over 
water,  more  gas  escaped  than  entered,  so  that  the  level  of 
the  water  rose  in  the  cylinder,  Graham  was  led  to  make 
his  experiments  on  the  diffusion  of  gases,  and  also  on  the 
rate  of  the  escape  of  gases  through  narrow  openings. 
Both  sets  of  experiments  led  to  the  same  law,  viz.  that 
the  rates  of  escape  are  inversely  proportional  to  the  square 
roots  of  the  densities  of  the  gases.  Under  equal  physical 
conditions,  hydrogen  moves  four  times  as  quickly  as 
oxygen,  which  is  sixteen  times  as  heavy  as  the  former. 
And  since  the  densities  are  proportional  to  the  weights  of 


THE  GREAT  LONDON  CHEMISTS  63 

the  molecules,  it  follows  that  a  molecule  of  hydrogen 
moves  through  space  four  times  as  rapidly  as  a  molecule 
of  oxygen.  This  law  was  confirmed  by  measurements 
made  on  many  other  gases.  These  experimental  re- 
searches of  Graham's  have  been  one  of  the  chief  supports 
of  the  kinetic  theory,  devised  long  afterwards,  on  the 
assumptions  that  the  pressure  of  gases  is  due  to  the  im- 
pacts of  their  molecules  on  the  walls  of  the  containing 
vessel,  and  that  their  temperature  is  to  be  ascribed  to  the 
rate  of  motion  of  the  molecules. 

Much  later,  in  1849,  Graham  investigated  the  rate  of 
flow  of  gases  through  narrow  tubes,  and  obtained  results 
which  have  also  been  found  of  incalculable  service  to  the 
theory  of  gaseous  matter. 

A  few  years  later,  in  1851  and  1852,  Graham  published 
investigations  on  the  diffusion  of  liquids,  a  subject  follow- 
ing close  on  the  lines  of  his  former  work  on  the  diffusion 
of  gases.  His  plan  of  experiment  was  as  simple  as  it  was 
well  adapted  to  furnish  the  information  sought.  A  wide- 
mouthed  bottle  was  filled  with  the  solution  of  a  salt,  and 
placed  inside  a  wider  jar;  the  jar  was  then  carefully  filled 
with  water,  care  being  taken  not  to  disturb  the  level  of 
the  solution  in  the  bottle.  The  apparatus  was  then  left 
to  itself  for  a  considerable  time.  It  was  found  that  the 
salt  did  not  stay  within  the  bottle,  but  gradually  escaped 
into  the  jar.  The  amount  escaping  in  different  times  and 
at  different  temperatures  was  measured. 

Experiments  made  on  a  great  variety  of  substances  soon 
revealed  the  fact  that  some  substances  escape  much  more 
rapidly  than  others.  For  instance,  Graham  found  that  69 
parts  of  sulphuric  acid,  58  of  common  salt,  26  of 
sugar,  13  of  gum-arabic,  and  only  3  of  egg-albumen 
escape  in  equal  times,  other  circumstances  being  equal. 
Some  other  substances,  such  as  potassium  and  ammonium 
chlorides,  potassium  and  ammonium  nitrates,  magnesium 


64    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

and  zinc  sulphates,  take  equal  times  to  diffuse.  More- 
over, some  salts  may  be  decomposed  into  their  constitu- 
ents by  diffusion  ;  among  these  are  ordinary  alum,  where 
the  more  easily  diffusible  potassium  sulphate  passes  away 
from  the  less  quickly  diffusing  aluminium  sulphate. 
And  even  potassium  sulphate  itself  shows  signs  of 
yielding  potassium  hydroxide  and  sulphuric  acid  on 
diffusion. 

It  was  known  that  a  solution,  placed  on  the  outside  of 
a  porous  diaphragm,  on  the  inside  of  which  was  pure 
water,  tended  to  pass  through  the  septum;  and  if  the 
inner  vessel,  containing  the  water,  were  fitted  with  a 
pressure-gauge,  the  pressure  would  rise  in  the  interior. 
This  pressure  had  been  named  '  osmotic  pressure/ 
Graham  attempted  to  connect  this  phenomenon  with 
diffusion,  but  found  that  ordinary  salts,  as  well  as  sugar, 
tannin,  alcohol,  urea,  and  similar  bodies,  had  little  effect 
in  raising  pressure.  On  the  other  hand,  osmotic  pheno- 
mena were  well  marked  when  strong  acids,  or  tartaric, 
citric,  or  acetic  acids,  were  present  in  the  cell.  In  all 
cases  of  osmotic  pressure,  it  was  found  that  the  porous  cell 
was  strongly  attacked,  and  Graham  was  inclined  to  ascribe 
the  phenomenon  to  chemical  action.  It  is  in  all  pro- 
bability due  to  the  fact  that  such  diaphragms  present 
very  little  of  what  we  now  term  'semi-permeability'  to 
the  salts  in  question. 

From  the  year  1852  to  the  year  1861,  Graham's  duties 
at  the  Mint  absorbed  nearly  all  his  time,  so  that  there  is 
a  long  gap  in  the  series  of  his  publications.  But  in  the 
latter  years  he  published  the  results  of  experiments  on 
the  transpiration  of  liquids,  a  subject  which  has  lately 
been  successfully  treated  by  numerous  investigators. 
And  with  his  practical  bias,  Graham  devised  a  plan  of 
applying  osmotic  phenomena  to  the  separation  of 
crystalline  substances,  which  easily  pass  through  a 


THE  GREAT  LONDON  CHEMISTS  65 

porous  diaphragm,  such  as  the  common  acids  and  salts, 
from  '  colloid '  or  gum-like  substances,  the  rate  of  passage 
of  which  is  much  slower.  Especially  useful  was  this  pro- 
cess for  the  separation  of  poisons  such  as  the  alkaloids 
and  metallic  salts  from  the  contents  of  the  stomach  in 
medico-legal  inquiries. 

Time  allows  me  only  to  mention  Graham's  most  in- 
teresting experiments  on  the  absorption  of  gases  by 
metals,  and  the  passage  of  hydrogen  through  a  thin  sheet 
of  palladium;  the  retention  of  hydrogen  by  palladium 
led  him  to  surmise  that  the  metallic  substance  was  a 
true  alloy  of  palladium,  with  metallic  hydrogen,  and  to 
form  the  theory  that  hydrogen  itself  should  be  ranked 
among  the  metals.  He  even  tried  to  impress  the  view  by 
terming  the  element  '  hydrogenium,'  in  consonance  with 
the  nomenclature  of  most  metals. 

But  I  must  conclude  this  imperfect  sketch  of  Graham's 
work,  trusting  that  what  I  have  said  may  induce  some  of 
my  readers  to  make  acquaintance  with  it  at  first  hand. 
Graham's  conscientiousness  in  all  he  did,  his  enthusiasm, 
and  his  great  ability  render  his  style  in  writing  a  most 
fascinating  one;  and  his  papers  will  always  remain  a 
model  to  those  who  publish  on  similar  subjects.  He 
possessed  a  truly  philosophical  mind  ;  and  in  this  he  more 
resembled  Boyle,  than  Cavendish  or  Davy.  Indeed,  it 
may  be  guessed  that  if  Graham  had  lived  in  the  seven- 
teenth century,  and  Boyle  in  the  nineteenth,  the  results  of 
their  labours  would  not  have  differed  very  widely  from 
those  which  bear  their  respective  names. 

Contrasting  Graham's  character  with  those  of  Cavendish 
and  Davy,  it  may  be  said  that  while  Cavendish  carried  his 
devotion  to  science  to  such  a  height  that  it  deprived  him  of 
the  ordinary  pleasures  of  a  human  being,  and  while  Davy 
took  perhaps  too  prominent  a  part  in  the  world  of  fashion 

E 


66    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

to  escape  the  accusation  of  'playing  to  the  gallery/ 
Graham  pursued  a  happy  mean,  beloved  by  the  few  whom 
he  chose  for  his  intimate  friends,  and  esteemed  and 
respected  by  all.  Of  him,  as  of  Faraday,  it  might  have 
been  said  with  no  shade  of  misgiving, '  He  was  a  good  and 
a  true  man.' 


JOSEPH  BLACK:  HIS  LIFE  AND  WOKK 

THERE  are  some  natures  so  happily  constituted  that  they 
escape  many  of  the  trials  which  beset  most  men.  Marcus 
Aurelius  thanked  his  adopted  father  for  having  taught 
him  the  advantages  of '  a  smooth  and  inoffensive  temper ; 
constancy  to  friends,  without  tiring  or  fondness;  being 
always  satisfied  and  cheerful ;  reaching  forward  into  the 
future,  and  managing  accordingly ;  not  neglecting  the  least 
concerns,  but  all  without  hurry,  or  being  embarrassed.' 
Such  a  character  had  Joseph  Black.  Dr.  Robison,  the  editor 
of  his  lectures,  his  successor  in  Glasgow  University,  and  his 
biographer,  wrote :  '  As  he  advanced  in  years  his  coun- 
tenance continued  to  preserve  that  pleasing  expression  of 
inward  satisfaction,  which,  by  giving  ease  to  the  beholder, 
never  fails  to  please.  His  manner  was  perfectly  easy  and 
unaffected  and  graceful.  He  was  of  most  easy  approach, 
affable,  and  readily  entered  into  conversation,  whether 
serious  or  trivial.  His  mind  being  abundantly  furnished 
with  matter,  his  conversation  was  at  all  times  pertinent 
and  agreeable.  He  was  a  stranger  to  none  of  the  elegant 
accomplishments  of  life.'  His  friend  Dr.  Ferguson  said  of 
him :  '  As  Dr.  Black  had  never  anything  for  ostentation, 
he  was  at  all  times  precisely  what  the  occasion  required , 
and  no  more.  Never  did  any  one  see  Dr.  Black  hurried  at 
one  time  to  recover  matter  which  had  been  improperly 
neglected  on  a  former  occasion.  Everything  being  done  in 
its  proper  season  and  place,  he  ever  seemed  to  have  leisure 
in  store ;  and  he  was  ready  to  receive  his  friend  or  acquaint- 
ance, and  to  take  his  part  with  cheerfulness  in  any  con- 

67 


68    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

versation  that  occurred.'  His  successor,  Dr.  Thomas 
Thomson,  found  Dr.  Robison's  estimate  of  Black's  char- 
acter so  just  that  he  appropriated  it  almost  verbatim  in 
his  History  of  Chemistry  without  the  formality  of  quota- 
tion marks. 

His  pupil,  Henry  Brougham,  one  of  the  founders  of  the 
college  in  which  I  have  the  honour  to  hold  a  chair,  por- 
trays him  in  his  Philosophers  of  the  time  of  George  III. 
as  'a  person  whose  opinions  on  every  subject  were  marked 
by  calmness  and  sagacity,  wholly  free  from  both  passion 
and  prejudice,  while  affectation  was  only  known  to  him 
from  the  comedies  he  might  have  read.  His  temper  in 
all  the  circumstances  of  life  was  unruffled.  .  .  .  The  sound- 
ness of  his  judgment  on  all  matters,  whether  of  literature 
or  of  a  more  ordinary  description,  was  described  by  Adam 
Smith,  who  said  he  "  had  less  nonsense  in  his  head  than 
any  man  living." '  Brougham,  writing  as  an  old  man, 
said:  'I  love  to  linger  over  these  recollections,  and  to 
dwell  on  the  delight  which  I  well  remember  thrilled  me 
as  I  heard  this  illustrious  sage  detail  the  steps  by  which 
he  made  his  discoveries,  illustrating  them  with  anecdotes 
sometimes  recalled  to  his  mind  by  the  passages  of  the 
moment,  and  giving  them  demonstration  by  performing 
before  us  the  many  experiments  which  had  revealed  to 
him  first  the  most  important  secrets  of  nature.  Next  to 
the  delight  of  having  actually  stood  by  him  when  his 
victory  was  gained,  we  found  the  exquisite  gratification  of 
hearing  him  simply,  most  gracefully,  in  the  calm  spirit  of 
philosophy,  with  the  most  perfect  modesty,  recount  his 
difficulties,  and  how  they  were  overcome;  open  to  us  the 
steps  by  which  he  had  successfully  advanced  from  one 
part  to  another  of  his  brilliant  course ;  go  over  the  same 
ground,  as  it  were,  in  our  presence,  which  he  had  for  the 
first  time  trod  so  many  long  years  before ;  hold  up  per- 
haps the  very  instruments  he  had  then  used,  and  act  over 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      69 

again  the  same  part  before  our  eyes  which  had  laid  the 
deep  and  broad  foundations  of  his  imperishable  renown. 
Not  a  little  of  this  extreme  interest  certainly  belonged  to 
the  accident  that  he  had  so  long  survived  the  period  of 
his  success — that  we  knew  there  sat  in  our  presence  the 
man  now  in  his  old  age  reposing  under  the  laurels  won 
in  his  early  youth.  But  take  it  altogether,  the  effect  was 
such  as  cannot  well  be  conceived.  I  have  heard  the 
greatest  understandings  of  the  age  giving  forth  their 
efforts  in  its  most  eloquent  tongues — have  heard  the  com- 
manding periods  of  Pitt's  majestic  oratory — the  vehe- 
mence of  Fox's  burning  declamation — have  followed  the 
close  compacted  chain  of  Grant's  pure  reasoning — been 
carried  away  by  the  mingled  fancy,  epigram,  and  argu- 
mentation of  Plunket;  but  I  should  without  hesitation 
prefer,  for  mere  intellectual  gratification  (though  aware 
how  much  of  it  is  derived  from  association)  to  be  once 
more  allowed  the  privilege  which  I  in  those  days  enjoyed 
of  being  present  while  the  first  philosopher  of  his  age  was 
the  historian  of  his  own  discoveries,  and  be  an  eye-witness 
of  those  experiments  by  which  he  had  formerly  made 
them,  once  more  performed  with  his  own  hands.' 

Truly,  Scotland  in  the  last  half  of  the  eighteenth 
century  was  the  home  of  many  great  men.  Adam  Smith, 
the  first  political  economist ;  David  Hume,  the  historian ; 
James  Hutton,  the  geologist;  and  James  Watt,  the 
engineer :  all  these  were  intimate  friends  of  Black's,  and 
each  in  his  way  was  an  originator  of  the  first  order. 
And  it  is  my  pleasant  task  to  present  to  you  an  account 
of  Black's  discoveries  and  their  consequences,  and  to 
attempt  to  show  that  his  work  began  a  new  epoch  for 
chemistry  and  physics. 

There  is  little  to  tell  of  Black's  early  history;  nor, 
indeed,  was  his  life  even  remotely  adventurous.  His 
career  may  be  told  in  a  few  words. 


70    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Joseph  Black  was  born  on  the  banks  of  the  Garonne, 
near  Bordeaux,  in  1728.  His  father,  John  Black,  was  a 
native  of  Belfast,  descended  from  a  Scottish  family  which 
had  settled  there;  he  resided  at  Bordeaux,  where  he 
carried  on  a  business  in  wine ;  he  was  an  intimate  friend 
of  President  Montesquieu.  Joseph  was  one  of  thirteen 
children,  of  whom  eight  were  sons.  In  1740,  at  the  age 
of  twelve,  he  was  sent  to  school  in  Belfast ;  and  like  many 
other  boys  of  the  north  of  Ireland,  he  crossed  to  Glasgow  to 
attend  its  University,  for  in  those  days,  of  course,  Queen's 
College,  Belfast,  had  not  been  founded.  This  was  in  the 
year  1746.  Dr.  Robison  mentions  letters  from  Mr.  Black 
to  his  son  Joseph,  from  which  it  would  appear  that  he  was 
in  every  respect  a  satisfactory  son  and  a  diligent  student. 
He  received  a  general  education ;  we  find,  at  least,  that  he 
could  write  good  Latin ;  and  he  was  taught  ethics  by 
Adam  Smith.  His  leanings  for  natural  science,  however, 
were  probably  encouraged  by  his  intimate  friendship  with 
the  son  of  the  Professor  of  Natural  Philosophy,  Dr.  Robert 
Dick,  later  successor  to  his  father  in  the  chair,  who,  un- 
fortunately, occupied  it  only  a  few  years,  for  he  was  early 
cut  off  by  death.  Black  also  owed  much  to  Cullen,  of  whom 
a  very  interesting  account  is  given  by  Thomas  Thomson 
in  his  History.  Cullen  was  Lecturer  in  Chemistry  in 
the  University  of  Glasgow  from  1746  to  1756 ;  and  in' 
1751  he  was  appointed  Professor  of  Medicine;  at  that  time, 
and,  indeed,  until  Thomas  Thomson  taught  chemistry, 
that  subject  was  taught  only  by  a  lecturer.  Thomson 
attributes  to  Cullen  a  singular  talent  for  arrangement,  dis- 
tinctness of  enunciation,  vivacity  of  manner,  and  profound 
knowledge  of  his  science — in  short,  enthusiasm — qualities 
which  made  him  adored  by  his  students.  He  took 
especial  pains  to  gain  their  friendship  by  frequent  social 
intercourse  with  them,  and  no  doubt  early  recognised 
Black's  great  promise.  Cullen's  single  contribution  to 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      71 

chemico-physical  literature  dealt  with  the  boiling  of  ether 
on  the  reduction  of  pressure,  and  its  growing  cold  during 
the  process.  The  reason  of  this  behaviour,  however,  was 
later  discovered  by  Black,  for  Cullen  confined  himself  to 
recording  the  observation.  It  was  not  long  before  Black 
rendered  help  to  Cullen  as  his  assistant ;  and  Black's  name 
was  frequently  quoted  by  Cullen  in  his  lectures  as  an 
authority  for  certain  facts. 

Black's  methodical  habits  led  him  to  keep  a  sort  of 
commonplace  book,  in  which  not  merely  the  results  of 
his  experimental  work  was  entered,  but  also  notes  on 
medicine,  jurisprudence,  or  matters  of  taste;  and  he 
practised  'double  entry/  for  he  also  kept  separate  journals 
in  which  these  notes  were  distributed  according  to  their 
subjects.  From  these  notebooks  the  dates  of  his  most 
important  discoveries  can  be  traced. 

Chemistry,  in  these  days,  was  handmaid  to  medicine ; 
the  influence  of  the  iatro-chemists,  founded  by  Paracelsus, 
still  held  its  sway,  although  certain  bold  investigators — 
among  them  Boyle,  Mayow,  and  Hales — a  century  before, 
had  shaken  themselves  free  from  its  thraldom.  And  the 
lectureship  on  chemistry  in  Glasgow  was  regarded  as  a 
step  to  a  more  remunerative  position,  and  was  held,  along 
with  the  Crown  professorship  of  medicine,  by  Cullen  from 
1751  to  1756.  It  was  probably  owing  to  Cullen's  advice 
that  Black  went  to  Edinburgh  in  1750  or  1751  to  finish 
his  medical  studies ;  perhaps  another  reason  may  be  found 
in  his  having  had  a  cousin  in  the  University,  Mr.  James 
Russel,  as  Professor  of  Natural  Philosophy,  with  whom  he 
lived.  There  he  took  the  degree  of  doctor  of  medicine  in 
1754.  It  is  true  that  he  might  have  graduated  in  Glasgow 
three  years  earlier ;  but  no  doubt  his  thoroughness  made 
him  wish  to  offer  a  thesis  worthy  of  praise,  and  it  was 
this  thesis  which  established  his  reputation.  More  of 
this  hereafter. 


72    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

In  1756  Dr.  Cullen  was  called  to  fill  the  Chair  of 
Chemistry  in  Edinburgh,  and  Black,  who  had  been  prac- 
tising as  a  physician  since  he  had  graduated,  was  called  to 
succeed  him  in  the  Chair  of  Anatomy  and  the  lectureship 
in  Chemistry;  for  his  reputation  in  the  subject  which  he 
had  made  his  own  was  even  then  a  high  one.  Black  did 
not  retain  the  Chair  of  Anatomy  for  long,  however ;  his 
tastes  lay  more  in  the  direction  of  medicine ;  and  with  the 
concurrence  of  the  University  he  and  the  professor  of 
medicine  exchanged  chairs.  While  he  held  these  offices 
he  also  engaged  in  medical  practice ;  and  Robison  says  that 
his  countenance  at  that  time  of  life — he  was  then  about 
thirty-two — was  equally  engaging  as  his  manners  were 
attractive ;  and  in  the  general  popularity  of  his  character 
he  was  in  particular  a  favourite  with  the  ladies.  No  one, 
so  far  as  we  know,  was  singled  out  by  his  preference ;  and 
to  the  end  of  his  days  he  remained  unmarried.  It  appears 
that  the  ladies  regarded  themselves  as  honoured  by  his 
attentions,  and  we  are  told  that  these  attentions  were  not 
indiscriminately  bestowed,  but  exclusively  on  those  who 
evinced  a  superiority  in  mental  accomplishments  or 
propriety  of  demeanour,  and  in  grace  and  elegance  of 
manners. 

In  1766,  Dr.  Cullen  exchanged  the  Chair  of  Chemistry 
at  Edinburgh  for  that  of  Medicine ;  and  with  one  accord 
University  and  town  united  in  calling  Dr.  Black  to  the 
vacant  chair.  Indeed,  in  1756,  he  had  been  recom- 
mended for  the  chair  by  the  University;  but  the  Town 
Councillors  who  were  the  electors  did  not  agree  with 
the  recommendation,  and  Cullen  was  appointed.  Now, 
however,  unanimity  prevailed,  and  Black  removed  to 
Edinburgh,  where  he  spent  the  rest  of  his  days. 

From  this  date,  he  devoted  himself  to  tuition,  and 
spared  no  pains  to  make  his  lectures  attractive  and 
useful.  He  illustrated  them  by  numerous  experiments. 


OF 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      73 

Robison  tells  us  that,  '  while  he  scorned  the  quackery  of 
a  showman,  the  simplicity,  neatness,  and  elegance  with 
which  they  were  performed  were  truly  admirable/  And 
Brougham  also  praises  his  manipulation.  'I  have  seen 
him/  he  writes,  'pour  boiling  water  or  boiling  acid  from 
one  vessel  to  another,  from  a  vessel  that  had  no  spout 
into  a  tube,  holding  it  at  such  a  distance  as  made  the 
stream's  diameter  small,  and  so  vertical  that  not  a  drop 
was  spilt.  The  long  table  on  which  the  different  pro- 
cesses had  been  carried  on  was  as  clean  at  the  end  of  the 
lecture  as  it  had  been  before  the  apparatus  was  planted 
upon  it.  Not  a  drop  of  liquid,  not  a  grain  of  dust 
remained/ 

Black  had  a  profound  influence  on  the  attitude  of  the 
Edinburgh  public  towards  science.  The  reputation  which 
he  established  as  a  lecturer  induced  many  to  attend  his 
lectures  without  any  particular  wish  to  learn  chemistry, 
but  merely  to  enjoy  an  intellectual  treat  ;  and  it  became 
the  fashion  to  hear  him. 

The  study  of  the  chemistry  of  gases,  after  Black's  dis- 
covery of  carbonic  acid,  made  rapid  progress;  but  Black 
did  not  take  part  in  its  advance.  His  health  had  never 
been  good;  he  was  very  subject  to  dyspepsia;  and  on 
several  occasions  his  lungs  or  his  bronchise  appear  to  have 
narrowly  escaped  being  affected,  for  he  was  troubled  with 
spitting  of  blood.  But  he  had  learned  the  lesson  —  yva>0e 
o-eavrov  —  know  thyself;  and  he  regulated  his  exercise  and 
his  diet  with  the  result  that  he  lived  a  quiet,  and  a  fairly 
long  life.  'Happy  is  the  nation  that  has  no  history'; 
and  Dr.  Black's  uneventful  life  was  passed  in  happiness. 
He  held  his  chair  for  more  than  thirty  years,  and  grew 
old  gracefully,  living  amongst  many  intimate  friends. 
He  at  one  time  acquired  a  reputation  for  parsimony  ;  but 
Brougham,  while  suggesting  a  reason  for  this  report, 
namely  that  he  kept  a  pair  of  scales  on  his  study  table 


74    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

with  which  he  used  to  weigh  the  guineas  paid  in  as  fees, 
defends  this  perhaps  somewhat  curious  practice,  and 
refutes  the  imputation ;  and  Robison,  who  also  alludes  to 
it,  states  in  a  footnote  that  he  could  give  more  than  one 
or  two  instances  in  which  a  great  part  of  Black's  fortune 
was  at  risk  for  a  friend. 

As  his  strength  decreased,  the  care  of  his  health 
occupied  more  and  more  of  his  attention;  he  became 
more  and  more  abstemious  in  his  diet.  One  of  his 
intimate  friends,  Dr.  Ferguson,  gives  the  following  account 
of  his  death,  one  worthy  of  such  a  calm  and  placid  philo- 
sopher: 'On  the  26th  November  1799,  and  in  the 
seventy- first  year  of  his  age,  he  expired,  without  any 
convulsion,  shock,  or  stupor  to  announce  or  retard  the 
approach  of  death.  Being  at  table,  with  his  usual  fare, 
some  bread,  a  few  prunes,  and  a  measured  quantity  of 
milk,  diluted  with  water,  and  having  the  cup  in  his  hand 
when  the  last  stroke  of  his  pulse  was  to  be  given,  he  had 
set  it  down  on  his  knees,  which  were  joined  together,  and 
kept  it  steady  with  his  hand  in  the  manner  of  a  person 
perfectly  at  ease,  and  in  this  attitude  expired,  without 
spilling  a  drop,  and  without  a  writhe  in  his  countenance, 
as  if  an  experiment  had  been  required  to  show  his  friends 
the  facility  with  which  he  departed.' 

He  left  more  money  than  any  one  thought  he  could 
have  acquired  in  the  course  of  his  career.  His  will  was  a 
somewhat  fantastic  one ;  he  divided  his  property  into  ten 
thousand  shares ;  and  he  distributed  it  among  numerous 
individuals  in  shares  or  in  fractions  of  shares,  according  to 
his  conception  of  their  needs  or  deserts. 

A  tale  is  told  in  Kay's  Edinburgh  Portraits  of  Black  and 
Hutton,  who  were  almost  inseparable  cronies.  Having  had 
a  disquisition  as  to  the  waste  of  food,  it  occurred  to  them 
that  while  testaceous  marine  animals  were  much  esteemed 
as  an  article  of  diet,  those  of  the  land  were  neglected ; 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      75 

they  resolved  to  put  their  views  in  practice,  and  having 
collected  a  number  of  snails,  had  them  cooked,  and  sat 
down  to  the  banquet.  Each  began  to  eat  very  gingerly ; 
neither  liked  to  confess  his  true  feelings  to  the  other. 
'Dr.  Black  at  length  broke  the  ice,  but  in  a  delicate 
manner,  as  if  to  sound  the  opinion  of  his  messmate: 
"Doctor,"  he  said,  in  his  precise  and  quiet  manner, 
"Doctor,  do  you  not  think  that  they  taste  a  little — a 
very  little  queer?" — "Queer, — queer  indeed! — tak  them 
awa',  tak  them  awa' ! "  vociferated  Dr.  Hutton,  start- 
ing up  from  table,  and  giving  vent  to  his  feelings  of 
abhorrence.' 

The  portraits  of  the  subject  of  this  biography  reveal 
Black  as  possessing  a  calm,  contemplative  nature;  but 
Kay's  caricatures  indicate  that  he  could  take  a  some- 
what humorous  view  of  life,  and  perhaps  might  even 
display  a  vein  of  caustic  sarcasm.  A  portrait  of  him 
while  lecturing  may  well  have  been  sketched,  we  may 
suppose,  while  he  was  making  scathing  comments  on 
the  objections  raised  by  a  German  chemist  named  Meyer 
to  his  doctrine  of  causticity,  which  '  that  person,'  as 
Brougham  tells  us, '  explained  by  supposing  an  acid,  called 
by  him  acidum  pingue,  to  be  the  cause  of  alkaline  mild- 
ness. The  unsparing  severity  of  the  lecture  in  which 
Black  exposed  the  ignorance  and  dogmatism  of  this 
foolish  reasoner  cannot  well  be  forgotten  by  his  hearers.' 
It  appears  to  me,  however,  that  Meyer's  theory  cannot 
have  been  correctly  stated  by  Brougham  (for  it  is  remark- 
ably like  Black's  own  explanation),  or  must  have  been 
misunderstood  by  Black.  Another  of  Kay's  portraits 
exhibits  Black  and  Hutton,  under  the  title  of  'The 
Philosophers ' ;  and  here  again  the  caricaturist  has  made 
it  obvious  that  Black  could  appreciate  a  joke.  A  third 
portrait  represents  him  taking  a  gentle  walk ;  it  conveys 
an  idea  of  his  appearance  in  his  fifty -ninth  year. 


76    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

The  portrait  of  Dr.  Cullen,  Black's  predecessor  both 
in  Glasgow  and  Edinburgh,  and  his  life-long  friend, 
is  also  given  by  Kay.  Cullen  died  in  1790,  at  the  age 
of  eighty-one. 

In  the  olden  days  it  was  considered  quite  as  marvellous 
that  a  gas  could  be  made  to  occupy  a  small  volume,  or 
that '  air '  could  be  produced  in  quantity  from  a  stone,  as 
that  an  Arabian  'djinn'  of  enormous  size  and  ferocious 
mien  could  issue  from  a  bottle,  as  related  in  the  '  Tale  of  a 
Fisherman,'  one  of  the  charming  stories  of  the  Arabian 
Nights  Entertainments.  It  is  true  that  in  the  middle  of 
the  seventeenth  century  Robert  Boyle  had  enunciated  his 
famous  discovery,  '  Touching  the  Spring  of  the  Air ' ;  in 
which  he  proved  that  the  greater  the  pressure  to  which  a 
gas  is  exposed  the  smaller  the  volume  it  will  occupy. 
But  however  great  the  pressure,  Boyle's  air  remained  air. 
It  might  have  been  thought  that  the  boiling  of  water  into 
steam  should  have  convinced  men  that  a  liquid,  at  least, 
could  be  changed  into  a  gas;  but  the  fact  that  steam 
changed  back  to  water  probably  prevented  attention  being 
paid  to  its  comparative  large  volume  while  hot.  It  was 
Black's  discovery  of  the  production  of  carbonic  acid  gas 
from  marble,  or  as  he  named  it,  'fixed  air,'  which  first 
directed  notice  to  this  possibility  of  the  production  of  a 
gas  from  a  solid;  and  further,  the  peculiar  property  of 
this  gas — its  power  of  being  fixed — was  one  which  com- 
pletely differentiated  it  from  ordinary  air.  Stephen  Hales 
the  botanist,  it  is  true,  had  distilled  many  substances  of 
vegetable,  animal,  and  mineral  origin;  among  them  he 
treated  many  which  must  have  produced  impure  hydrogen, 
marsh-gas,  carbonic  acid  gas,  and  oxygen;  but  Hales 
contented  himself  with  measuring  the  volume  of  gases 
obtained  from  a  known  weight  of  material,  without  con- 
cerning himself  about  their  properties.  And  as  the  result 
of  many  experiments,  he  concluded  that  '  our  atmosphere 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      7*7 

is  a  chaos,  consisting  not  only  of  elastick,  but  also  of 
unelastick  air-particles,  which  in  plenty  float  in  it,  as  well 
as  the  sulphureous,  saline,  watry,  and  earthy  particles, 
which  are  no  ways  capable  of  being  thrown  off  into  a 
permanently  elastick  state,  like  those  particles  which 
constitute  true  permanent  air/  This  was  the  current 
belief  as  regards  the  nature  of  air. 

The  cause  which  gave  rise  to  Black's  famous  research  is 
a  curious  one.  Sir  Robert  Walpole,  as  well  as  his  brother 
Horace,  afterwards  Lord  Walpole,  were  troubled  with  the 
stone.  They  imagined  that  they  had  received  benefit 
from  a  medicine  invented  by  a  Mrs.  Joanna  Stephens; 
and  through  their  influence  she  received  five  thousand 
pounds  for  revealing  the  secret,  which  was  published  in 
the  London  Gazette  on  the  19th  June  1739.  It  was 
described  as  follows : — 

'My  medicines  are  a  Powder,  a  Decoction,  and  Pills. 
The  powder  consists  of  Egg-shells1  and  Snails,2  both 
calcined.  The  decoction  is  made  by  boiling  some  Herbs 3 
(together  with  a  Ball,  which  consists  of  Soap,4  Swines'- 
Cresses,  burnt  to  a  Blackness,  and  Honey)  in  water.  The 
Pills  consist  of  Snails  calcined,  Wild  Carrot  seeds,  Burdock 
seeds,  Ashen  Keys,  Hips  and  Hawes,  all  burnt  to  a  Black- 
ness, Soap  and  Honey.' 

Dr.  Cullen  and  his  colleagues  held  opposing  views  as  to 
the  efficacy  of  such  quaint  and  caustic  remedies ;  and  it 
was  with  the  object  of  discovering  a  '  milder  alkali,'  and 
bringing  it  into  the  service  of  medicine,  that  Black  began 

1  '  Egg-shells  and  Snails  calcined  in  a  crucible  surrounded  with  coal  for 
8  hours.     Then  left  in  an  earthenware  pan  to  slake  in  a  dry  room  for  2 
months.    The  Shells  thus  become  of  a  milder  taste,  and  fall  into  powder.' 

2  '  Snails  left  in  a  crucible  until  they  have  done  smoaking,  then  rubbed 
up  in  a  mortar.     Take  6  parts  of  Egg-shell  to  1  of  Snail-powder.     Snails 
ought  only  to  be  prepared  in  May,  June,  July,  and  August.' 

3  '  Herbs  of  decoction  :  Green  Chamomile,  Sweet  Fennel,  Parsley,  and 
Burdock  ;  leaves  or  roots.' 

4  'Soap:  Best  Alicant  Soap.' 


78    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

his  experiments  on  magnesia.  They  are  described  in  a 
paper  entitled  '  Experiments  upon  Magnesia  Alba,  Quick- 
lime, and  some  other  Alcaline  Substances';  it  was  the 
chemical  contents  of  his  thesis  for  the  degree  of  M.D., 
which  he  took  at  Edinburgh  in  1754 ;  he  had  been  making 
the  experiments  since  1752.  The  actual  thesis  was  in 
Latin :  '  De  Humore  Acido  a  Cibis  orto,  et  Magnesia  Alba ' ; 
the  pamphlet  was  published  in  the  following  year. 

The  medicines  in  vogue  as  solvents  of  the  urinary  cal- 
culus were  all  caustic ;  the  lapis  infernalis,  or  caustic 
potash,  and  the  ley  of  the  soap-boilers,  or  caustic  soda. 
These  substances  are  made  from  mild  alkali,  or  carbonates, 
by  boiling  their  solutions  with  slaked  lime,  itself  produced 
by  slaking  quicklime  with  water.  Now  quicklime  is 
formed  by  heating  lime-stone  in  the  fire;  it  thereby 
acquires  its  burning  properties,  or  causticity ;  and  this  it 
was  supposed  to  derive  from  the  fire,  of  which  it  absorbed, 
as  it  were,  the  essence.  The  act  of  boiling  the  mild 
alkalies  with  lime  was  supposed  to  result  in  a  transference 
of  this  educt  of  fire  to  the  alkalies,  which  themselves 
became  caustic,  Lime-water,  or  a  solution  of  caustic  lime 
was  used  as  a  solvent  for  the  calculus;  and  it  was  an 
attempt  to  produce  a  less  caustic  solvent  from  Epsom  salts 
that  induced  Black  to  begin  his  researches. 

As  his  notes  show,  Black  began  by  holding  the  old  view. 
He  attempted  to  catch  the  igneous  matter  as  it  escaped 
from  lime,  as  it  becomes  '  mild '  on  exposure  to  the  air : 
he  appears  to  have  made  some  experiment  with  this  view ; 
but  his  comment  was,  'Nothing  escapes — the  cup  rises 
considerably  by  absorbing  air/  Two  pages  further  on  in 
his  notebook  he  records  an  experiment  to  compare  the 
loss  of  weight  sustained  by  an  ounce  of  chalk  when  it  is 
calcined  with  its  loss  when  dissolved  in  '  spirit  of  salt/  or 
hydrochloric  acid ;  and  he  then  evidently  began  to  suspect 
the  reason  of '  mildness '  and  '  causticity/ 


JOSEPH  BLACK :  HIS  LIFE  AND  WORK      79 

Another  memorandum,  a  few  pages  later,  shows  that  he 
had  solved  the  mystery.  '  When  I  precipitate  lime  by  a 
common  alkali  there  is  no  effervescence.  The  air  quits 
the  alkali  for  the  lime,  but  it  is  not  lime  any  longer,  but 
c.c.c.  It  now  effervesces,  which  good  lime  will  not.' 

But  we  must  trace  the  chain  of  reasoning  which  led  him 
to  come  to  this  conclusion. 

Having  prepared  '  mild '  magnesia  by  mixing  Epsom 
salt  or  sulphate  of  magnesia  with  carbonate  of  potash,  or 
'  pearl- ashes/  he  found  that  it  is  '  quickly  dissolved  with 
violent  effervescence  or  explosion  of  air  by  the  acids  of 
vitriol,  nitre,  and  of  common  salt,  and  by  distilled  vinegar ' ; 
that  the  properties  of  these  salts — the  sulphate,  nitrate, 
chloride,  and  acetate  of  magnesium — differ  greatly  from 
those  of  the  common  alkaline  earths;  that  when  boiled 
with  'salt-ammoniac,'  or  chloride  of  ammonium,  volatile 
crystals  of  smelling-salts  were  deposited  on  the  neck  of 
the  retort,  which,  on  mixing  with  the  chloride  of  mag- 
nesium remaining  in  the  retort,  reproduced  the  'mild' 
magnesia;  that  a  similar  effect  is  produced  by  boiling 
'  mild '  magnesia  with  '  any  calcareous  substance ' ;  while 
the  acid  quits  the  calcareous  salt  to  unite  with  the  mag- 
nesia, '  mild '  magnesia  is  again  precipitated  on  addition  of 
a  dissolved  alkali. 

On  igniting  '  mild '  magnesia,  it  changed  into  a  white 
powder,  which  dissolved  in  acids  without  effervescence. 
And  the  process  of  ignition  had  deprived  it  of  seven- 
twelfths  of  its  weight.  Black  next  turned  his  attention  to 
the  volatile  part ;  he  attempted  to  restore  it  by  dissolving 
the  magnesia  in  a  sufficient  quantity  of  '  spirit  of  vitriol ' 
or  dilute  sulphuric  acid,  and  separated  it  again  by  the 
addition  of  alkali.  The  resulting  white  powder  now  effer- 
vesced violently  with  acids,  and  'recovered  all  those 
properties  which  it  had  lost  by  calcination.  It  had 
acquired  besides  an  addition  of  weight  nearly  equal  to 


80    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

what  had  been  lost  in  the  fire;  and  as  it  is  found  to 
effervesce  with  acids,  part  of  the  addition  must  certainly 
be  air.' 

Black  here  made  an  enormous  stride ;  he  had  weighed 
a  gas  in  combination.  He  argues  further :  '  It  seems  there- 
fore evident  that  the  air  was  forced  from  the  alkali  by  the 
acid,  and  lodged  itself  in  the  magnesia/  We  may  repre- 
sent the  change  diagrammatically  thus : 

Magnesia  \    x  Alkali^-Yitriolated  alkali. 
Spirit  of  vitriol   '     ^  Air->Mild  magnesia. 

The  next  step  was  to  try  whether  mild  magnesia  lost 
the  same  weight  on  being  mixed  with  acid  as  it  did  when 
heated  in  the  fire.  But  owing  probably  to  the  solubility 
of  the  fixed  air  in  the  water,  a  much  less  loss  was  found 
on  dissolving  the  magnesia  (35  grains  out  of  120)  than  by 
heating  it  (78  grains  out  of  120).  The  amount  of  acid 
required  to  expel  the  fixed  air  was,  however,  practically 
the  same  as  that  required  to  dissolve  the  magnesia  usta, 
or  heated  magnesia  (267  and  262  grains). 

Turning  his  attention  next  to  chalk,  he  dissolved  some 
in  muriatic  acid,  and  having  precipitated  with  fixed  alkali 
no  difference  could  be  detected  between  the  recovered  and 
the  original  chalk.  He  had  thus  first  separated  the  fixed 
air  from  the  chalk,  and  then  recombined  the  two.  These 
experiments  led  Black  to  conclude  that  fixed  air  must  be 
of  the  nature  of  an  acid,  for  it  converts  quick-lime — the 
acrid  earth,  as  he  termed  it — into  crude  lime,  or  mild 
earth,  the  mildness  being  due  to  its  union  with  fixed  air. 

The  explanation  is  thus  given  of  the  curious  fact  that 
mild  magnesia,  mixed  with  lime-water,  gives  pure  water ; 
for  the  fixed  air  leaves  the  magnesia  and  unites  itself  to 
the  lime,  and  both  the  magnesia  usta  and  the  chalk 
which  are  formed  are  insoluble  in  water.  And  the  action 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      81 

of  quick-lime  in  causticising  alkali  is  similarly  explained 
by  its  removing  the  fixed  air  from  the  alkali,  thus  render- 
ing the  latter  caustic,  while  itself  becoming  mild. 

Reasoning  further,  Black  foresaw  that  caustic  alkali, 
added  to  Epsom  salt  or  vitriolated  magnesia,  should  give 
a  precipitate  of  magnesia  which  should  not  effervesce  with 
acids,  for  here  fixed  air  is  excluded ;  and,  also,  that  caustic 
alkali  should  separate  from  acids  lime  in  the  quick  state, 
only  united  with  water. 

Similar  experiments  of  treating  chalk  with  acids  and 
heating  it,  which  had  been  performed  with  magnesia, 
showed  similar  results. 

But  it  had  yet  to  be  demonstrated  that  fixed  air  did  not 
share  the  properties  of  ordinary  atmospheric  air.  So 
Black  placed  four  fluid  ounces  of  lime-water,  as  well  as 
four  ounces  of  common  water,  under  the  receiver  of  an 
air-pump,  and  exhausted  the  air;  air  rose  from  each  in 
about  the  same  quantity ;  it  therefore  appeared  that  the 
air  which  quick-lime  attracts  is  of  a  different  kind  from 
that  which  is  mixed  with  water.  Quick-lime  does  not 
attract  air  when  in  its  most  ordinary  form,  but  is  capable 
of  being  joined  to  one  particular  species  only,  'which  is 
dispersed  through  the  atmosphere,  either  in  the  state  of  a 
very  subtle  powder,  or,  more  probably,  in  that  of  an  elastic 
fluid.  To  this  I  have  given  the  name  of  fixed  air,  and 
perhaps  very  improperly ;  but  I  thought  it  better  to  use  a 
word  already  familiar  in  philosophy  than  to  invent  a  new 
name,  before  we  be  more  fully  acquainted  with  the  nature 
and  properties  of  this  substance.' 

The  next  step  was  to  examine  the  nature  of  caustic 
alkali,  and  to  prove  whether  it  gained  weight  on  being 
made  '  mild.'  This  was  achieved  indirectly,  by  finding  the 
amount  of  acid  required  to  neutralise  the  same  weight  of 
caustic  alkali,  and  '  salt  of  tartar ' — what  we  know  as 
potassium  carbonate.  Six  measures  of  acid  were  required 

F 


82    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

to  saturate  the  former,  and  five  the  latter ;  and  Black  was 
very  near  the  truth ;  indeed  his  error  was  only  about  four 
per  cent.  He  proved,  by  addition  of  sulphuric  acid,  that 
the  caustic  alkali  contained  no  lime,  and  therefore  that 
its  causticity  was  not  due  to  an  admixture  of  that 
substance. 

To  prove  that  lime-stone,  or  magnesia,  '  loses  its  air ' 
when  dissolved  in  an  acid,  but  regains  it  on  addition  of  a 
mild  alkali,  the  acid  in  which  the  lime  was  dissolved 
passing  to  the  alkali,  Black  added  caustic  ley  to  a  solution 
of  Epsom  salt,  the  result  being  a  precipitate  of  magnesia ; 
this  dissolved  in  vitriol  without  effervescence,  showing 
that  no  fixed  air  had  taken  part  in  the  change.  He  also, 
on  adding  caustic  alkali  to  a  solution  of  chalk  in  spirit  of 
salt  (or  hydrochloric  acid),  produced  lime,  which  on  being 
dissolved  in  water  produced  lime-water,  indistinguishable 
from  that  produced  from  quick-lime  and  water.  He  goes 
on  to  say  that '  had  we  a  method  of  separating  the  fixed 
alkali  from  an  acid,  without  at  the  same  time  saturating 
it  with  "  air  "  we  should  then  obtain  it  in  a  caustic  form.' 
It  can  be  done,  it  is  true,  by  heating  nitre  with  charcoal, 
but  the  alkali  is  then  found  saturated  with  air;  and 
again,  by  heating  the  alkali-salts  of  vegetable  acids,  the 
same  occurs.  Black  conjectures  that  the  fixed  air  must 
be  derived  either  from  the  nitre  or  the  charcoal  in  the 
first  case  (indeed  it  is  derived  from  both,  the  nitre  supply- 
ing the  oxygen  to  the  carbon);  and  in  the  second,  he 
remarks  that  the  vegetable  acid  is  not  really  separated, 
but  rather  destroyed  by  the  fire.  How  nearly  he  came 
to  the  discovery  that  fixed  air  is  produced  from  carbon ! 

Such  was  Black's  research  on  fixed  air.  And  now 
having  shown  that  a  gas  can  be  retained  by  a  solid,  and 
can  be  made  to  escape  by  treatment  with  acid  or  by  heat, 
he  attacked  somewhat  later  the  problem  of  the  cause  of 
this  fixation.  He  discovered  it  to  be  due  to  what  he 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      83 

termed  '  latent '  or  hidden  heat.  But  his  research  was  not 
made  with  this  object;  the  connection  of  the  two  was 
fortuitous,  although  of  a  fundamental  nature. 

Between  the  years  1759  and  1763,  he  formed  opinions 
regarding  the  quantity  of  heat  necessary  to  raise  equally 
the  temperatures  of  different  substances.  Boerhaave 
imagined  that  all  equal  portions  of  space  contain  equal 
amounts  of  heat,  irrespective  of  the  nature  of  the  matter 
with  which  they  are  filled ;  and  his  reason  for  this  state- 
ment was  that  the  thermometer  stands  at  the  same 
height  if  placed  in  contact  with  objects  near  each  other. 
Here  we  have  a  confusion  between  heat  and  temperature ; 
and  this  was  perceived  by  Black,  for  he  pointed  out  that 
a  distinction  must  be  drawn  between  quantity  and  inten- 
sity of  heat :  the  latter  being  what  we  now  call  tempera- 
ture.  He  quotes  Fahrenheit  to  show  that  while  equal 
measures  of  water  at  different  temperatures  acquire  a 
mean  temperature  when  mixed,  it  requires  three  measures 
of  quicksilver  at  a  high  temperature  to  convert  two 
measures  of  water  at  a  low  temperature  to  the  mean  of 
the  two  temperatures;  and  this  corresponds  to  twenty 
times  the  weight  of  the  water.  Black  expressed  this  by 
the  statement  that  the  capacity  for  heat  of  quicksilver  is 
much  less  than  that  of  water. 

But  before  this,  in  1757,  Black  had  made  experiments 
leading  up  to  these  views.  He  had  noticed  that  when  ice 
or  any  solid  substance  is  changing  into  a  fluid,  it  receives 
a  much  greater  amount  of  heat  than  what  is  perceptible 
in  it  immediately  afterwards  by  the  thermometer.  A 
great  quantity  of  heat  enters  into  it  without  making  it 
perceptibly  warmer.  Conversely,  in  freezing  water  or  any 
liquid,  a  large  amount  of  heat  comes  out  of  it,  which  again 
is  not  revealed  by  a  thermometer. 

He  then  proceeded  to  estimate  the  quantity  of  heat 
which  had  to  be  absorbed  by  a  known  weight  of  ice  in 


84    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

order  to  melfc  it.  He  hung  up  two  globes  side  by  side, 
about  18  inches  apart,  in  a  large  empty  hall,  in  which  the 
temperature  remained  practically  constant ;  each  globe 
contained  5  ounces ;  one  of  ice  at  32°  F.,  the  other  water 
at  33°.  The  latter  had  a  delicate  thermometer  suspended 
in  it.  The  temperature  of  the  hall  was  47°  F.  In  half  an 
hour,  the  water  had  attained  the  temperature  40°  F. ; 
and  the  ice  took  ten  hours  and  a  half  to  attain  the  same 
temperature,  that  is,  twenty-one  times  as  long  as  the 
water.  The  heat,  which  the  ice  absorbed  during  melting 
was  (40  —  33)  x  21  or  147  units;  that  is,  had  it  been 
absorbed  by  the  five  ounces  of  water  it  would  have  made 
it  warmer  by  147°.  The  temperature  of  the  ice,  however, 
was  8°  warmer  than  its  melting-point,  after  the  21  half- 
hours  ;  hence  139  or  140  '  degrees  had  been  absorbed 
by  the  melting  ice,  and  were  concealed  in  the  water  into 
which  it  had  changed.' 

The  method  of  experiment  was  next  varied.  Black 
weighed  a  lump  of  ice,  and  added  it  to  a  weighed  quantity 
of  warm  water  of  which  the  temperature  was  known. 
The  warm  water  was  cooled  to  a  much  lower  degree  by 
the  melting  of  the  ice,  than  if  it  had  been  mixed  with  a 
quantity  of  water  of  32°  F.,  equal  in  weight  to  the  ice. 
The  quantity  of  heat  absorbed  by  the  ice  in  melting  ap- 
peared from  this  second  experiment  to  have  been  capable 
of  heating  an  equal  quantity  of  water  through  143°  F. 

A  third  experiment  was  made,  in  which  it  was  proved 
that  a  lump  of  ice,  placed  in  an  equal  weight  of  water  at 
176°,  lowered  the  temperature  of  the  water  to  32°.  Now 
176  —  32=144° — again  a  similar  result.  The  latent  heat 
of  water  is  therefore  about  142  or  143,  in  Fahrenheit 
units.  The  result  of  the  most  careful  measurements  give 
79*5°  centigrade  units,  which  corresponds  with  143°  units 
of  Fahrenheit's  scale.  Curiously  enough,  this  fundamental 
datum  has  not  yet  been  determined  with  the  accuracy 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      85 

which  is  customary  nowadays,  and  it  is  still  uncertain  to 
one  seven-hundredth  of  its  value.  Black's  determination 
was  a  remarkably  good  one,  especially  if  we  consider  the 
crude  appliances  which  he  used. 

The  substance  of  this  research  was  communicated  to 
the  '  Philosophical  Club/  or  Society  of  Professors  and 
others  in  the  University  of  Glasgow  in  the  year  1762,  and 
was  expounded  yearly  by  Black  in  his  lectures  to  his 
students. 

Black  suggested  to  Irvin,  his  pupil,  and  afterwards  his 
successor  in  the  Glasgow  chair,  to  determine  the  latent 
heat  of  fusion  of  spermaceti  and  bees'-wax  ;  and  he  found 
that  these  substances,  too,  absorb  heat,  insensible  to  the 
thermometer,  on  assuming  the  liquid  state.  In  this 
manner,  he  made  his  thesis  general.  But  in  attempting 
to  extend  it  beyond  the  case  of  liquids  and  solids,  he  went 
astray.  For  example,  he  imagined  that  the  great  rise  of 
temperature,  which  may  even  reach  redness,  caused  by  the 
hammering  of  iron  by  a  skilled  smith,  was  due  to  the 
'  extrication  of  the  latent  heat  of  the  iron  by  hammering/ 
He  did  not  realise  that  heat  can  be  produced  from 
mechanical  work;  that  work  can  be  quantitatively  trans- 
formed into  heat;  a  discovery  made  more  than  eighty 
years  later,  by  Joule,  although  it  had  been  anticipated  by 
Count  Rumford,  and  by  Sir  Humphry  Davy,  in  the  begin- 
ning of  last  century. 

Similar  experiments  were  made  by  Black  on  the  latent 
heat  of  steam,  in  which  he  compared  the  time  required  for 
a  known  weight  of  water  to  rise  through  a  definite  interval 
of  temperature  when  exposed  to  a  constant  supply  of  heat 
with  that  required  to  dissipate  the  water  into  steam,  But 
his  estimate  of  830  units  required  to  evaporate  one  part  of 
water  was  not  so  accurate ;  the  actual  figure  is  967  units  on 
the  Fahrenheit  scale.  Black  cited  experiments  by  Boyle, 
by  Robison,  his  successor  in  the  Glasgow  chair,  and  by 


86    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Cullen,  his  predecessor,  in  which  the  boiling-point  of 
liquids  had  been  found  to  be  lowered  by  reduction  of 
pressure;  he  rightly  ascribes  this  to  the  freer  escape  of 
the  vapour,  and  to  the  absorption  of  heat  by  the  vapour, 
and  the  consequent  cooling  of  the  liquid  from  which  it  is 
escaping. 

These  conceptions  of  Black's  were  utilised  by  his  friend 
James  Watt  in'  his  work  on  condensers,  and,  as  every  one 
knows,  effected  a  revolution  in  the  structure  of  steam- 
engines,  and  as  a  consequence  in  the  whole  of  our  indus- 
trial and  social  life ;  and  further,  they  were  developed  by 
many  men  of  science,  until  in  the  hands  of  the  masters — 
Joule,  Clerk-Maxwell,  Rankine,  James  Thomson,  and 
Kelvin,  on  the  physical  side,  and  of  Willard  Gibbs,  the 
American,  on  the  chemical  side — they  form  the  very 
groundwork  of  the  sister  sciences,  physics  and  chemistry. 

Black's  great  chemical  discovery  that  a  gas  exists  which 
is  clearly  not  a  modification  of  atmospheric  air,  seeing  it 
can  be  '  fixed '  by  alkalies  and  alkaline  earths,  led  the  way 
to  '  pneumatic  chemistry,'  as  it  was  called,  and  was  followed 
by  the  discovery  of  oxygen  by  Priestley,  of  nitrogen  by 
Rutherford,  of  hydrogen  by  Cavendish  and  Watt,  and  of 
the  more  recent  discoveries  of  argon  and  its  congeners,  all 
of  them  constituents  of  the  atmosphere.  In  fact,  the  gases 
of  the  atmosphere  have  been  discovered  entirely  by  Scots- 
men and  Englishmen.1 

And  Black's  proof,  that  the  change  of  a  complex  com- 
pound to  simpler  compounds,  and  the  building  up  of  a 
complex  compound  from  simpler  ones,  can  be  followed 
successfully  by  the  use  of  the  balance,  has  had  for  its 
consequence  the  whole  development  of  chemistry.  It  is 
only  in  the  most  recent  years,  since  Becquerel  observed 
the  effect  of  uranium  ores  and  salts  in  discharging  an 

1  In  justice  to  the  Swede  Scheele,  it  should  be  said  that  his  discovery 
of  oxygen  was  contemporaneous  with  Priestley's. 


JOSEPH  BLACK:  HIS  LIFE  AND  WORK      87 

electroscope,  and  since  Madame  Curie  discerned  one  of 
the  causes  of  the  discharge  by  uranium  ore,  namely,  the 
existence  in  it  of  a  new  element,  radium,  and  since  Ruther- 
ford and  Soddy's  isolation  of  the  gases  evolved  from 
radium  and  from  thorium,  that  a  new  and  more  sensi- 
tive instrument  has  been  placed  at  the  disposal  of 
chemists  in  the  electroscope.  We  are  at  the  beginning  of 
a  new  era.  Every  discovery  of  a  new  principle  of  research 
heralds  a  new  departure;  and  the  compound  nature  of 
many  of  the  so-called  elements  begins  to  appear  from 
their  electrical  behaviour,  in  much  the  same  manner  as 
Black  demonstrated  the  decomposability  of  compounds  in 
the  year  1752. 


LORD   KELVIN 

ON  June  16,  1896,  there  took  place  in  the  University  of 
Glasgow  an  almost  unique  ceremony.  On  that  day 
the  jubilee  of  Lord  Kelvin  was  celebrated ;  he  had  been 
Professor  of  Natural  Philosophy  at  Glasgow  University 
for  fifty  years.  The  Prince  of  Wales,  now  King  Edward, 
sent  him  a  letter  of  congratulation ;  twenty-eight  univer- 
sities, twelve  colleges,  and  fifty- one  learned  societies 
sent  delegates  with  addresses,  wishing  Lord  Kelvin  many 
more  years  of  health  and  happiness,  and  mentioning  in 
terms  of  profound  admiration  his  magnificent  achieve- 
ments in  the  domain  of  physics.  What  were  these,  and 
why  did  they  deserve  and  obtain  such  universal  admira- 
tion ?  To  answer  that  question  fully  would  require  a 
much  longer  space  than  is  at  my  disposal;  but  I  shall 
try  to  give  a  short  sketch  of  William  Thomson's  life  and 
work. 

In  1812,  James  Thomson,  William's  father,  was  a  teacher 
in  the  Royal  Academic  Institute  of  Belfast.  He  was  one 
of  the  descendants  of  a  number  of  Scotsmen  who  emigrated 
to  North  Ireland  in  the  seventeenth  and  eighteenth 
centuries.  He  had  two  sons,  James  and  William,  both  of 
whom  were  born  in  Ireland,  and  both  of  whom  became 
illustrious.  When  William  was  eight  years  old,  his  father 
was  appointed  to  the  Chair  of  Mathematics  in  the  Uni- 
versity of  Glasgow.  My  father  was  one  of  his  students ; 
and  I  remember  well  his  allusions  to  Professor  Thomson's 
kindliness  and  sense  of  humour. 


90    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

It  was"  his  habit  to  cross-examine  his  students,  at  the 
beginning  of  each  lecture,  on  the  subject  of  the  preceding 
day's  work ;  and  it  was  customary  in  his  junior  class  to 
begin  with  very  elementary  questions.  One  day  he  asked 
a  certain  Highlander  :  '  Mr.  M'Tavish,  what  do  you  under- 
stand by  a  "  point "  ? '  The  answer  was,  '  It 's  just  a  dab  ! ' 
Again,  Mr.  M'Tavish  was  asked,  in  the  course  of  the  con- 
struction of  some  diagram :  '  What  should  I  do,  Mr. 
M'Tavish  ? '  '  Tak  a  chalk  in  your  hand/  '  And  next  ? ' 
'  Draw  a  line.'  Professor  Thomson  complied,  and  pausing, 
said :  '  How  far  shall  I  produce  the  line,  Mr.  M'Tavish  ? ' 
'  Ad  infinitum ! '  was  the  astounding  reply. 

At  the  mature  age  of  ten  William  entered  the  university. 
His  training  had  been  wholly  in  his  father's  hands ;  Pro- 
fessor Thomson  was  clear-sighted  enough  to  recognise  that 
he  had  two  very  remarkable  sons.  They  were  brought  up 
on  Classics  and  Mathematics,  Logic  and  Philosophy. 

In  May  1907,  at  the  annual  dinner  of  the  London 
'  Glasgow  University  Club,'  I  had  the  good  fortune  to  hear 
Lord  Kelvin  express  his  views  on  education.  His  theme 
was  the  '  University  of  Glasgow ' ;  and  he  commended  the 
universality  of  the  training  which  it  used  to  give.  By  the 
age  of  twelve,  said  he,  a  boy  should  have  learned  to  write 
his  own  language  with  accuracy  and  some  elegance;  he 
should  have  a  reading  knowledge  of  French,  should  be 
able  to  translate  Latin  and  easy  Greek  authors,  and  should 
have  some  acquaintance  with  German.  '  Having  learned 
thus  the  meaning  of  words/  continued  Lord  Kelvin, '  a  boy 
should  study  Logic/  In  his  charming  discursive  style,  he 
went  on  to  descant  on  the  advantages  of  a  knowledge  of 
Greek.  '  I  never  found,'  he  said,  '  that  the  small  amount 
of  Greek  I  learned  was  a  hindrance  to  my  acquiring  some 
knowledge  of  Natural  Philosophy/  It  certainly  was  not 
in  his  case.  And  it  may  here  be  remarked  that  it  is  surely 
a  mistake  to  lay  down  a  hard  and  fast  rule  that  no  youth 


LORD  KELVIN  91 

should  enter  a  college  until  he  has  reached  the  age  of 
fifteen  or  sixteen;  William  Thomson  took  the  highest 
prizes  in  Mathematics  and  Physics  before  he  reached  that 
age.  It  may  be  said  that  his  precocity  was  phenomenal ; 
no  doubt  it  was;  but  it  is  precisely  those  boys  who  are 
unique  and  unlike  their  fellows  who  are  of  value  to  the 
race,  and  every  chance  should  be  given  to  exceptional 
talent. 

Although  William  Thomson  spent  six  years  at  Glasgow 
University,  he  did  not  graduate :  in  those  days  the  aim  of 
a  student's  ambition  was  not  a  degree,  but  the  acquisition 
of  knowledge.  Before  he  had  reached  the  age  of  seventeen, 
he  went  to  Cambridge,  where  he  passed  four  years.  There 
the  examination  system  was  in  full  swing;  and  to  the 
disgrace  of  the  examiners,  Thomson  was  not  the  '  Senior 
Wrangler ';  he  was  not  regarded  as  the  best  mathematician 
of  his  year ;  and  this,  in  spite  of  the  remark  made  by  one 
of  his  examiners,  that  '  the  Senior  Wrangler  was  not  fit 
to  cut  pencils  for  Thomson.'  It  is  known  that  success  in 
this  examination  depends  largely  on  rapidity  in  writing 
and  on  accuracy  of  memory,  ratter  than  on  originality ; 
and  the  tale  is  told  that  on  Thomson's  '  coach/  or  tutor, 
asking  him  why  he  had  spent  so  much  time  in  answering  a 
particular  question,  he  replied  that  he  had  to  think  it  all 
out  from  first  principles.  '  But  it  is  a  problem  of  your  own 
discovery/  said  the  coach.  Thomson  had  to  confess  that 
he  had  quite  forgotten  his  own  handiwork, and  that  while  his 
competitor  had  learned  the  answer  by  heart,  Thomson  had 
had  to  rediscover  the  solution.  However,  he  was  successful 
in  gaining  the  '  Smith's  Prize/  a  reward  for  inventiveness 
rather  than  memory.  That  same  year,  he  was  elected 
Fellow  of  his  College,  and  had  an  income  of  about  £200, 
which  enabled  him  to  continue  his  studies  in  France. 

While  at  Cambridge,  Thomson  was  not  only  a  student ; 
he  always  took  a  keen  interest  in  music,  and  was  president 


92    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

of  the  Musical  Society ;  he  also  carried  off  the  '  Colquhoun 
sculls '  for  his  excellence  as  an  oarsman.  In  those  days 
the  science  of  Cambridge  was  fettered  by  the  bonds  which 
Newton  had  imposed.  It  is  unfortunate,  though  perhaps 
natural,  that  to  the  advent  of  a  great  man  a  period  of 
stagnation  succeeds.  It  was  thus  with  the  Schoolmen, 
who  subsisted  for  many  centuries  on  the  philosophy  of 
Aristotle;  and  the  science  of  Cambridge,  in  1845,  was 
based  on  the  work  of  Newton,  nearly  a  century  and  a  half 
old.  Indeed,  the  spirit  was  that  of  Timseus,  in  Plato's 
dialogue,  who  said :  '  If  we  wish  to  acquire  any  real 
acquaintance  with  astronomy,  we  shall  let  the  heavenly 
bodies  alone/  In  fact,  Bacon's  advice  to  proceed  by  way 
of  experiment  and  induction  had  been  forgotten.  Needless 
to  say,  this  reproach  has  long  been  removed,  by  the  labours 
of  Clerk-Maxwell,  Rayleigh,  Stokes,  and  J.  J.  Thomson. 
In  the  'forties  Paris  was  the  home  of  Fourier,  Fresnel, 
Ampere,  Arago,  Biot,  and  Regnault,  all  physicists  and 
mathematicians  of  the  highest  rank  ;  and  Thomson  spent 
a  year  working  in  Regnault's  laboratory,  where  experiments 
on  water  and  steam,  their  densities,  pressure,  and  specific 
heats,  were  being  carried  on  with  the  utmost  refinement. 
During  the  next  year,  1846,  the  Chair  of  Natural  Philosophy 
in  Glasgow  fell  vacant,  and,  to  their  credit,  the  Senate  of 
the  day  advised  Queen  Victoria  to  appoint  William 
Thomson,  then  a  youth  of  twenty- two,  as  professor. 
Never  was  a  choice  better  justified  in  its  results.  For 
Thomson,  by  example  and  by  precept,  trained  many 
students  to  be  a  credit  to  their  old  university,  and  carried 
out  in  cellars,  which  served  as  laboratories,  and  which 
were  situated  almost  next  door  to  that  in  which  James 
Watt  invented  the  condensing  engine,  almost  all  his 
numerous  and  important  investigations. 

Thomson  was  not  what  would  be  called  a  good  lecturer ; 
he  was  too  discursive.     I  doubt  whether  any  man  with  a 


LORD  KELVIN  93 

brain  so  much  above  the  ordinary,  so  much  more  rapid  in 
action  than  the  average,  can  be  a  first-rate  teacher. 
Certainly,  in  my  own  case,  I  gained  much  more  in  my 
second  than  in  my  first  year's  attendance.  But  Thomson 
never  allowed  the  interest  of  his  students  to  flag ;  his 
aptness  in  illustration  and  his  vigour  of  language  prevented 
that.  Lecturing  one  day  on  '  Couples,'  he  explained  how 
forces  must  be  applied  to  constitute  a  couple,  and  illus- 
trated the  direction  of  the  forces  by  turning  round  the 
gas-bracket.  This  led  to  a  discussion  on  the  miserable 
quality  of  Glasgow  coal-gas,  and  how  it  might  be  improved. 
Following  again  the  main  idea,  he  caught  hold  of  the 
door,  and  swung  it  to  and  fro ;  but,  again,  his  mind 
diverged  to  the  difference  in  the  structure  of  English  and 
Scottish  doors.  We  never  forgot  what  a  couple  was ;  but 
— the  idea  might  have  been  conveyed  more  succinctly. 
He  held  strong  views  on  the  'absurd,  ridiculous,  time- 
wasting,  soul-destroying  system  of  British  weights  and 
measures  ' ;  and  in  spite  of  all  the  efforts  of  the  '  Decimal 
Association,'  we,  the  Americans,  and  the  Russians  remain 
examples  of  irrational  conservatism  in  respect  of  the 
awkwardness  of  our  systems. 

The  Cartesian  method  of  locating  a  point  was  indelibly 
impressed  on  my  memory  by  the  following  incident:  A 
student,  whose  position  was  roughly  about  the  centre  of 
the  lecture-room,  made  that  noise  so  disturbing  to  a 
lecturer,  yet  so  difficult  to  locate,  caused  by  gently  rubbing 
the  sole  of  his  foot  on  the  floor.  '  Mr.  Macfarlane  ! '  said 
Sir  William.  Mr.  Macfarlane,  the  fides  Achates,  came, 
received  a  whispered  communication,  and  went  out  of  the 
room.  In  about  ten  minutes  he  returned  with  a  tape-line, 
and  proceeded  to  measure  a  length  along  one  wall,  on 
which  he  made  a  pencil-mark.  He  then  measured  out  at 
right  angles  another  length,  and  made  a  chalk-mark  on 
the  floor,  erecting  on  it  a  pointer.  '  Mr.  Smith,  it  was  you 


94    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

who  made  that  noise :  be  so  good  as  to  leave  the  room/ 
said  Sir  William.  Mr.  Smith  blushed  and  retired.  Then 
came  the  explanation.  Mr.  Macfarlane  had  gone  below 
the  sloping  tier  of  seats;  had  accurately  diagnosed  the 
precise  position  of  Mr.  Smith's  erring  foot,  and  had 
accurately  measured  the  distance  from  the  two  walls. 
These  measurements  were  reproduced  in  full  view  of  the 
students,  and  the  advantages  of  the  system  of  Cartesian 
co-ordinates  were  experimentally  demonstrated,  while 
justice  was  satisfied. 

Owing  to  an  accident,  Sir  William  was  lame ;  but  it  did 
not  interfere  with  his  activity  of  body.  Indeed,  it  lent 
emphasis  to  his  amusing  class  demonstration  of  '  uniform 
velocity,'  when  he  inarched  backwards  and  forwards 
behind  his  lecture-bench,  with  as  even  a  movement  as  his 
lameness  would  permit ;  and  the  class  generally  burst  into 
enthusiastic  applause  when  he  altered  his  pace,  and  intro- 
duced us  to  the  meaning  of  the  word  '  acceleration.' 

In  his  laboratory  Sir  William  was  a  most  stimulating 
teacher,  though  his  methods  were  not  those  which  have 
since  been  introduced  into  physical  laboratories.  I  re- 
member that  my  first  exercise,  which  occupied  over  a 
week,  was  to  take  the  kinks  out  of  a  bundle  of  copper 
wire.  Having  achieved  this  with  some  success,  I  was 
placed  opposite  a  quadrant  electrometer  and  made  to 
study  its  construction  and  use.  I  was  made  to  determine 
the  potential  difference  between  all  kinds  of  materials, 
charged  and  uncharged ;  and  among  others  between  the 
external  and  internal  coatings  of  a  child's  balloon,  black- 
leaded  externally  and  internally,  and  filled  with  hydrogen. 
Nor  was  the  Professor  always  prescient.  On  one  occasion 
I  turned  the  handle  of  a  large  electrical  machine,  while 
he  held  a  two-gallon  Leiden  jar  by  its  knob,  and  charged 
the  outside  coating.  It  was  not  until  it  was  fully  charged 
that  it  occurred  to  one  of  us  that  while  the  jar  was  quite 


LORD  KELVIN  95 

safe  as  long  as  it  was  in  his  hands,  it  was  impossible  for 
him  to  deposit  it  on  the  table  without  running  the  risk  of 
an  inconveniently  heavy  shock.  Finally,  after  rapid  de- 
liberation, two  of  us  held  a  towel  by  its  corners,  and  Sir 
William  dropped  the  jar  safely  into  the  middle ;  it  was 
then  possible  to  touch  the  outside  without  mishap.  In 
short  we  had  little  systematic  teaching,  but  were  at  once 
launched  into  knowledge  that  there  is  an  unknown  region 
where  much  is  to  be  discovered ;  and  we  were  made  to 
feel  that  we  too  might  help  to  fathom  its  depths. 
Although  this  method  is  not  without  its  disadvantages — 
for  systematic  instruction  is  of  much  value — there  is  much 
to  be  said  for  it.  On  the  one  hand,  too  long  a  course  of 
experimenting  on  old  and  well-known  lines,  as  is  now 
the  practice  among  teachers  of  science,  is  likely  to  imbue 
the  young  student  with  the  idea  that  all  physics  consists 
in  learning  the  use  of  apparatus,  and  in  repeating 
measurements  which  have  already  been  made.  On  the 
other  hand,  too  early  attempts  to  investigate  the  unknown 
are  likely  to  prove  fruitless  for  want  of  manipulative  skill, 
and  for  want  of  knowledge  of  what  has  already  been 
done.  The  best  of  all  possible  training,  however,  is  to 
serve  as  hands  for  a  fertile  brain — the  brain  of  one  who 
knows  what  he  wishes  to  discover,  who  is  familiar  with  all 
that  has  already  been  attempted,  and  who  gradually  trains 
his  assistant  to  take  part  in  the  thinking  as  well  as  in  the 
manipulation.  If  at  the  same  time  the  student  is  made 
to  read,  not  merely  concerning  the  problem  on  which  he 
is  immediately  engaged,  but  on  all  branches  of  his  sub- 
ject, nothing  can  be  better  than  such  stimulating  inter- 
course with  an  inventive  teacher  for  those  who  have  ability 
to  profit  by  it. 

It  is  extremely  difficult  to  explain  Lord  Kelvin's  contri- 
butions to  knowledge  to  those  who  have  not  themselves 
some  acquaintance  with  its  problems.  Let  me  begin  by  a 


96    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

quotation  from  Helmholtz,  late  Professor  of  Physics  in 
Berlin,  an  old  and  intimate  friend  of  Lord  Kelvin : 
'  His  peculiar  merit  consists  in  his  method  of  treating 
problems  of  mathematical  physics.  He  has  striven  with 
great  consistency  to  purify  the  mathematical  theory  from 
hypothetical  assumptions,  which  were  not  a  pure  expres- 
sion of  the  facts.  In  this  way  he  has  done  very  much  to 
destroy  the  old  unnatural  separation  between  experimental 
and  mathematical  physics,  and  to  reduce  the  latter  to  a 
precise  and  pure  expression  of  the  laws  of  the  phenomena. 
He  is  an  eminent  mathematician,  but  the  gift  to  translate 
real  facts  into  mathematical  equations,  and  vice  versa,  is 
by  far  more  rare  than  that  to  find  a  solution  of  a  given 
mathematical  problem,  and  in  this  direction  Sir  William 
Thomson  is  most  eminent  and  original.'  When  Lord 
Kelvin  began  his  work,  the  equivalence  of  heat  and 
energy  was  unrecognised;  forces  were  distinguished  as 
'  conservative '  and  '  unconservative ' ;  the  world  was  sup- 
posed to  be  filled  with  subtle  fluids  and  effluvia ;  and  it 
must  have  seemed  almost  hopeless  to  seek  any  general 
explanation  of  material  phenomena.  Light,  heat,  elec- 
tricity, magnetism,  and  chemical  action  were  all  regarded 
as  distinct  'forces,'  each  a  cause  of  change.  Thomson, 
and  his  collaborator  Tait,  the  late  Professor  of  Physics  in 
Edinburgh,  in  their  Treatise  on  Natural  PhilosopJty,  did 
much  to  emphasise  the  view  that  Physics  deals  with 
things,  not  theories  ;  with  relations,  not  with  their  mathe- 
matical expression,  equations ;  and  they  tried  successfully 
to  free  the  science  from  the  bonds  of  formal  mathematics. 
They  demonstrated  that  the  principle  of  '  Least  Action ' 
is  universal ;  that  by  its  help  it  is  possible  to  explain  the 
motions  of  the  planets  and  their  satellites,  of  wheels, 
lathes,  machines  of  all  kinds,  of  every  system  of  which 
we  can  define  the  moving  parts  and  the  forces  which  act 
on  them. 


LORD  KELVIN  97 

In  1893  Lord  Kelvin  gave  a  discourse  on  'Isoperi- 
metric  Problems '  at  the  Royal  Institution,  in  which  he 
attempted  to  describe  the  nature  of  this  general  problem ; 
it  is  that  technically  called  '  Determining  a'  minimum ' ; 
and  he  began  with  the  task  which  faced  Dido  of  old — to 
surround  the  most  valuable  piece  of  land  with  a  cowhide, 
i.e.  to  draw  the  shortest  possible  line  around  it.  A 
similar  problem  is,  to  build  a  railway-line  through 
undulating  country  at  the  smallest  possible  cost ;  and  one 
very  different  in  appearance,  but  related  to  those  already 
cited,  owing  to  Lord  Kelvin's  consummate  power  of  dis- 
covering analogies  between  phenomena  apparently  uncon- 
nected, is  the  condition  of  stability  of  water  rotating  in 
an  ellipsoidal  vessel,  and  a  number  of  similar  problems. 
Kelvin's  work  on  Elasticity  is  no  less  far-reaching ;  in 
Karl  Pearson's  great  treatise  on  that  subject,  no  less 
than  one  hundred  pages  are  filled  with  Kelvin's  con- 
tributions. 

Lord  Kelvin  was  also  the  author  of  a  theory  of  the 
nature  of  the  ultimate  particles  of  matter — the  atoms, 
lie  imagined  them  to  consist  of  'vortex  rings  in  the 
ether,'  the  ether  being  conceived  as  a  frictionless  fluid,  all- 
present,  even  filling  the  interstices  between  the  atoms,  or 
ultimate  particles  of  matter.  Yortex  rings  in  air,  some- 
times made  by  smokers,  are  elastic ;  they  cannot  be  cut 
without  being  destroyed ;  and,  in  a  frictionless  fluid,  their 
rotatory  motion  would  be  eternal,  if  once  impressed. 
Recent  discoveries  may  lead  to  the  modification  of  this 
theory  of  the  nature  of  matter ;  but  it  has  much  in  its 
favour. 

Kelvin  was  a  strong  partisan  of  Joule's  work  on  the 
equivalence  of  heat  and  work.  It  was  believed  up  to 
1850  that  the  heat  developed  on  compressing  a  gas  was 
'  caloric,'  squeezed  out  of  the  gas,  as  one  might  squeeze 
water  out  of  a  sponge  ;  but  Kelvin  taught  that  heat  must 

G 


98    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

be  due  to  the  motions  of  the  molecules  of  a  gas;  and 
that  when  the  gas  is  compressed,  the  impacts  of  its  mole- 
cules on  the  walls  of  the  containing  vessel  are  more 
numerous,  and  that  the  work  done  in  compressing  a  gas 
appears  as  heat,  owing  to  the  more  numerous  impacts  of 
its  molecules.  Following  on  this,  it  was  necessary  to 
Revise  an  absolute  scale  of  temperature,  and  that  we  also 
owe  to  Lord  Kelvin.  It  is  based  on  what  is  known  as  the 
'  Second  Law  of  Thermodynamics ' — that  heat  cannot  be 
transferred  from  a  cold  to  a  hot  body  without  expending 
work.  Following  these  ideas,  Lord  Kelvin  was  led  to 
consider  the  probable  age  of  the  earth,  based  on  an 
estimate  of  its  original  temperature,  and  the  rate  at  which 
heat  would  be  lost  by  radiation.  His  opinion  is  that  the 
earth  may  have  been  habitable  twenty  million  years  ago, 
but  could  not  have  been  habitable  as  long  ago  as  four 
hundred  million  years. 

The  province  of  electro-magnetism  owes  very  much  to 
Lord  Kelvin.  It  was  he  who  developed  the  medium  sug- 
gested by  Faraday  into  a  means  of  representing  electro- 
magnetic forces  by  analogy  with  the  distortion  of  an  elastic 
solid.  After  he  had  worked  out  in  this  manner  the  con- 
nection between  energy  and  electro-magnetism,  he  devised 
our  present  system  of  electrical  units — volts,  amperes, 
farads,  coulombs,  etc.,  and  invented  machines  to  deter- 
mine their  numerical  values.  If  it  be  permitted  to  assign 
their  relative  importance  to  his  contributions  to  practical 
science,  this  must  be  pronounced  the  greatest.  Without 
it  the  science  of  electricity  would  be  helpless  as  commerce 
without  a  monetary  system,  and  without  weights  and 
measures.  His  work  is  the  foundation  of  wireless  tele- 
graphy, and  of  many  applications  of  the  electric  current. 
It  was  he  who  taught  the  world  how  to  transmit  rapid 
and  trustworthy  signals  through  cables;  and  he  was  a 
pioneer  of  cable  telegraphy.  In  the  old  days  of  cables 


LOKD  KELVIN  99 

attempts  were  made  to  ensure  rapid  signalling  by  heavy 
currents;  but  Kelvin  showed  that  feeble  currents,  com- 
bined with  delicate  instruments,  made  the  difficulty  dis- 
appear. His  'siphon  recorder'  is  still  used,  and  cannot 
well  be  improved  on.  A  great  social  and  commercial 
revolution  dates  from  August  1858,  when  the  message 
was  signalled  under  the  ocean,  '  Europe  and  America  are 
united  by  telegraphic  communication.  "  Glory  to  God  in 
the  highest,  and  on  earth  peace,  goodwill  toward  men." ' 
This  revolution  owed  much  to  Sir  William  Thomson,  who 
never  lost  heart  and  never  faltered  in  the  belief  that  all 
difficulties  would  be  overcome.  His  presence  on  board 
ship  during  the  laying  of  the  first  Atlantic  cable  directed 
his  attention  towards  nautical  matters ;  and  to  him  we 
owe  a  deep-sea  sounding  apparatus,  and  a  compass  easily 
corrected  for  the  magnetic  deviations  produced  by  tlie 
iron  or  steel  used  in  the  construction  of  ships. 

We  must  not  estimate  Lord  Kelvin's  greatness,  how- 
ever, merely  by  his  own  discoveries  and  inventions,  great 
as  these  are ;  he  has  served  as  a  model  for  many  disciples. 
His  sincere  and  single-minded  devotion  to  truth;  his 
interest  in  the  work  of  others,  and  his  sympathy  with 
their  efforts;  his  fairness  of  mind  and  absence  of  pre- 
judice ;  and  his  straightforward  and  loving  character  have 
raised  the  ideals  of  the  whole  scientific  world,  and  have 
deeply  influenced  the  best  minds  in  all  countries.  His 
idea  of  <a  treasure  of  which  no  words  can  adequately 
describe  the  value '  is :  '  Goodwill,  kindness,  friendship, 
sympathy,  encouragement  for  more  work.'  It  is  to  such 
a  man  that  the  world  owes  an  eternal  debt  of  gratitude, 
and  he  it  was  for  whom  no  honour  that  men  have  it  in  their 
power  to  bestow  could  be  too  great.  It  is  pleasant  to  be 
able  to  state  that  Lord  Kelvin's  mental  energy  was  unim- 
paired by  his  burden  of  more  than  eighty  years.  He  was 
present  at  the  meeting  of  the  British  Association  at 


100    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Leicester  in  August  1907,  and  took  part  in  the  discussions 
on  the  '  Nature  of  the  Atom.'  The  minds  of  most  men, 
like  their  bodies,  grow  stiff  with  age  and  unreceptive  of 
new  impressions ;  but  Lord  Kelvin's  until  his  latest  days 
had  all  the  vigour  and  elasticity  of  a  young  man's.  We 
may  well  rejoice  that  he  was  spared  so  long  to  enrich  the 
world  with  his  wisdom  and  his  inimitable  example. 


PIERRE  EUGENE  MARCELLIN  BERTHELOT 

1827-1907 l 

MARCELLIN  BERTHELOT  was  a  native  of  Paris,  born  on 
October  25,  1827,  in  a  flat  looking  on  to  the  Rue  du 
Mouton,  situated  in  the  Place  de  Greve,  now,  owing  to  the 
activity  of  Baron  Haussmann,  the  Place  de  l'H6tel-de- 
Ville.  His  father,  a  doctor  of  medicine,  was  a  member  of 
the  sect  of  the  Jansenists,  a  small  branch  of  the  Gallic 
Catholic  Church.  He  was  a  serious  man,  impatient  with 
the  folly  of  his  concitoyens,  and  somewhat  depressed  by 
the  poverty  and  sufferings  of  his  patients.  The  '  Church 
of  Faith '  had  its  own  Liturgy,  and  the  congregation  joined 
in  singing  psalms  and  hymns.  Many  of  the  prdtres 
were  among  Dr.  Berthelot's  patients,  and  young  Berthelot 
must  often  have  listened  to  discussions  on  the  attempts, 
ultimately  successful,  to  substitute  the  Roman  for  the 
Gallic  liturgy.  Dr.  Berthelot  was  married  in  1826,  shortly 
after  starting  practice.  His  wife  was  a  lively,  bright 
woman,  who  transmitted  her  features  to  her  son. 

At  that  time,  Charles  the  Tenth  was  on  the  throne. 
The  allied  powers  had  involved  France  in  a  Gouverne- 
ment  de  Cures ;  and  it  was  part  of  the  State  Ceremonial 
to  form  a  procession,  which  was  headed  by  the  Holy 
Sacrament  and  the  Papal  Nuncio,  a  cardinal  in  red,  from 
the  Tuileries,  to  Notre  Dame  and  back,  and  in  which  the 
King,  the  Queen,  the  Dauphin  (who,  according  to  Madame 

1  A  notice  which  appeared  in  the  Proceedings  of  the  Royal  Society  for 
1907. 

101 


102    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Berthelot  mere,  was  able  to  look  behind  him  without  turn- 
ing his  head),  and  the  Court  took  part.  The  spectators, 
under  the  penalty  of  sacrilege,  were  obliged  to  kneel  as 
the  Corpus  Christi  procession  passed.  Those  who  refused 
were  prosecuted  and  severely  punished. 

Such  a  travesty  of  religion  was  not  to  Dr.  Berthelot's 
taste ;  the  bourgeoisie  was  liberal  and  imbued  with  the 
sentiments  of  Voltaire;  and  the  Berthelot  family  was  of 
the  bourgeois  class.  During  the  revolutions  of  1830  and 
1848,  their  house  commanded  a  full  view  of  one  of  the 
chief  scenes  of  operation,  and  young  Berthelot  must  have 
often  been  a  spectator  of  many  a  scene  of  disturbance  and 
violence.  Highly  developed  intellectually,  and  mentally 
impressionable,  his  later  convictions  were  doubtless  largely 
owing  to  his  early  surroundings. 

That  Marcellin  resembled  his  mother  in  features  has 
already  been  mentioned.  But  the  resemblance  was  not 
merely  external;  there  existed  between  them  the  most 
intimate  sympathy.  Their  favourite  promenade  was  in 
the  Bishop's  garden  behind  Notre  Dame,  along  the  Quays 
with  their  stalls  of  flowers,  and  in  the  Jardin  des  Plantes. 
Their  minds  were  both  quick  and  versatile;  they  were 
eagerly  interested  in  all  that  passed  around  them,  and,  as 
Madame  Berthelot  used  to  say  (borrowing  the  simile  from 
one  of  the  invasions  which  she  witnessed),  they  could  both 
'  drive  a  Russian  team  with  a  sure  hand  and  at  a  full 
gallop.'  The  writer,  who  knew  Berthelot  only  during  his 
later  years — since  1878 — never  conversed  with  any  one 
who  possessed  such  rapidity  of  thought.  Given  an  idea, 
with  his  quick  discursive  mind  he  would  follow  out  all 
possible  paths  and  by-ways,  seeing  the  consequences  of 
this  assumption  and  of  that,  interposing  occasionally  a 
quaint  remark,  not  exactly  humorous,  but  de  plaisanterie. 
He  was  a  delightful  conversationalist,  interested  and  in- 
tensely interesting,  willing  to  discuss  all  possible  subjects, 


PIERRE  EUGENE  MARCELLIN  BERTHELOT    103 

and  willing,  too,  to  hear  all  varieties  of  view,  even  those 
contrary  to  his  own  opinion. 

His  persistence,  energy  of  character,  and  devotion  to 
duty  were  inherited  from  his  father.  Berthelot  used  to 
regret  that  he  had  not  inherited  his  mother's  optimism. 
He  used  to  say  that  when  a  misfortune  overtook  her,  she 
had  what  the  French  call  a  crise  de  larmes,  soon  over 
and  followed  by  her  usual  optimistic  cheerfulness ;  that  a 
rainbow  generally  rose  through  her  tears,  and  that  she 
became  gaily  resigned  to  the  incurable  evil. 

After  the  demolition  of  the  Rue  du  Mouton,  the  family 
moved  to  Neuilly,  then  quite  in  the  country.  Renan  often 
looked  in  on  Sundays  as  a  guest  at  their  midday  meal. 
In  one  of  his  private  letters  he  tells  how  Berthelot  and 
he  became  friends.  He  had  just  renounced  his  clerical 
orders,  and  was  maUre-repetiteur  in  a  school,  where  he 
led  a  lonely  and  melancholy  existence,  depressed  by  the 
mental  struggles  which  he  had  come  through,  and  far 
from  his  family  and  his  native  Brittany.  One  day,  a 
pupil  about  four  years  younger  than  himself  accosted 
him;  the  talk  became  intimate,  and  a  friendship  with 
Berthelot  was  soon  formed,  destined  to  endure  for  life. 
Their  intercourse  was  frequent ;  begun  early,  when  both 
were  slender  youths,  never  a  year,  hardly  a  month,  passed 
without  their  seeing  each  other.  Renan  used  sometimes 
to  poke  fun  at  Berthelot;  the  tale  is  told  that,  passing  a 
cemetery,  Renan  said  to  him  :  '  La,  voici  la  seule  place  que 
tu  n'as  jamais  convoitee.'  Such  sallies  were  always  received 
with  amusement  and  good  temper.  On  another  occasion, 
provoked  by  the  remark  that  his  coat  was  worn  with  the 
air  of  a  cassock,  Renan  retorted  :  '  What  is  there  in  you, 
Marcellin,  that  gives  you  the  air  of  just  having  left  off 
fighting  behind  a  barricade  ? '  While  Berthelot  retained 
his  slender  form,  Renan  became  very  corpulent ;  Berthelot, 
nervous  and  active,  maintained  to  the  last  his  almost 


104    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

feverish  love  of  work;  Renan  was  meditative — almost  a 
dreamer.  It  was  Berthelot's  sad  duty  to  speak  of  his 
lost  friend  when  the  monument  at  Treguier  was  raised  to 
his  memory.  He  emphasised  Renan's  lucidity  even  to 
the  end,  his  power  of  work,  his  great  mental  activity ;  the 
words  were  applicable  with  equal  force  to  himself. 

Never  was  there  a  more  devoted  couple  than  Monsieur 
and  Madame  Berthelot.  After  he  had  ended  his  brilliant 
career  at  the  Lycee  Henri  iv.,  Berthelot  gained  the  prize 
of  honour  at  the  open  competition  in  1846.  Without  any 
coaching,  he  passed  successively  all  his  degrees — Bachelier, 
Licencie,  and  Docteur-es-Sciences ;  for  the  doctorate  he 
presented  a  somewhat  sensational  thesis,  entitled,  '  The 
Compounds  of  Glycerine  with  Acids,  and  the  Artificial 
Production  of  the  Natural  Fats.'  While  working  at  this 
research,  he  was  lecture-assistant  (preparateur)  to  Balard, 
at  the  College  de  France.  In  1861,  largely  through  the 
influence  of  Duruy,  then  Minister  of  Public  Instruction, 
Berthelot  was  promoted  to  the  Chair  of  Organic  Chemistry 
in  that  institution;  and  there  he  remained  all  his  life. 
In  that  year  he  was  awarded  by  the  Academy  of  Sciences 
the  Jecker  Prize  for  his  remarkable  researches  on  the 
artificial  production  of  organic  compounds  by  synthesis, 
and  at  the  same  time  the  Academy  recommended  the 
creation  of  the  special  chair  which  Berthelot  filled  so  long 
and  so  illustriously.  In  his  own  words:  'Adonne,  des 
mes  debuts  dans  la  vie,  au  culte  de  la  verite  pure,  je  ne 
me  suis  jamais  mele  a  la  lutte  des  interets  pratiques  qui 
divisent  les  hommes.  J'ai  vecu  dans  mon  laboratoire 
solitaire,  entoure  de  quelques  eleves,  mes  amis.' 

When  he  won  the  Jecker  Prize,  he  was  in  his  thirty- 
fifth  year.  The  appointment  to  the  Chair  at  the  College 
de  France  made  it  possible  for  him  to  marry  Mademoiselle 
Breguet,  the  daughter  of  a  French  Swiss,  whose  family 
had  made  money  by  manufacturing  watches,  famed  since 


PIERRE  EUGENE  MARCELLIN  BERTHELOT    105 

the  middle  of  last  century.  Monsieur  Breguet  was  a 
constructeur  industriel,  or  builder  of  factories.  He  lived 
near  the  Place  de  I'Hotel-de-Ville,  on  the  Quai  de 
1'Horloge,  and  the  families  were  acquainted  from  early 
days.  Mademoiselle  was  a  desirable  partie,  well-dowered, 
and  of  great  beauty,  which  she  retained  up  to  the  end  of 
her  life.  She  was  placid  in  manner,  with  lovely  eyes,  and 
a  brilliant  complexion,  rendered  even  more  striking,  when, 
at  an  advanced  age,  her  hair  was  silver ;  and  in  the  church 
of  Saint-Etienne  du  Mont  there  is  a  picture  of  Sainte- 
Helene,  the  lovely  face  of  which  is  taken  from  a  portrait 
of  Madame  Berthelot  as  a  girl.  The  meeting  of  the  young 
couple  was  somewhat  romantic  :  Mademoiselle  Breguet, 
no  doubt,  must  have  appeared  to  Marcellin  to  be  beyond 
his  reach,  and  besides,  his  attention  was  otherwise  occupied. 
But  one  day,  on  the  Pont  Neuf,  Mademoiselle  was  crossing 
the  longest  bridge  in  Paris  in  the  face  of  a  strong  wind, 
wearing  a  charming  Tuscan  hat,  then  the  mode.  Behind 
her  walked  her  future  husband ;  suddenly  she  turned 
round,  to  avoid  having  her  hat  blown  off,  and  practically 
ran  into  his  arms.  If  not  exactly  love  at  first  sight,  it 
was  a  case  of  love  at  first  touch.  Their  married  life  was 
of  the  happiest ;  indeed,  it  may  be  said  that  they  were  in 
love  with  each  other  till  the  end.  One  of  the  sons 
wrote:  ' Mon  pere  et  ma  mere  s'adoraient;  jamais  le 
rnoindre  nuage  n'avait  trouble  leur  bonheur.  Us  s'etaient 
compris  des  le  premier  jour.  Us  etaient  si  bien  faits  pour 
se  completer !  Bien  que  tres  lettree  et  fort  intelligente, 
maman  s'etait  toujours  effacee  devant  son  mari,  se  bornant 
a  s'efforcer  de  le  rendre  parfaitement  heureux.  C'etait, 
a  son  avis,  la  seule  fa9on  de  collaborer  a  son  ceuvre.' 
Another  intimate  friend  added:  'Monsieur  et  Madame 
Berthelot  s'adoraient;  tous  deux  etaient  de  la  nature 
d'elites ;  sa  compagne  n'avait  cesse  de  Fencourager  et  de 
le  soutenir.'  No  one  visiting  their  house  could  fail  to 


106    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

remark  this  absolute  devotion  to  each  other ;  never  was 
there  a  happier  family.  Although  not  a  conversationalist, 
Madame  Berthelot,  by  her  perfect  tact,  her  serene  manner, 
and  her  charming  sympathetic  face,  knew  how  to  make 
each  guest  appear  at  his  best;  the  ball  of  conversation 
was  lightly  tossed  round  the  table,  Berthelot  himself,  by 
his  quaint  and  paradoxical  remarks,  contributing  his 
share.  A  dinner  at  Berthelot's,  in  his  old  house  in  the 
Palais  Mazarin,  the  home  of  the  Institute,  was  a  thing  to 
be  remembered.  Always  charitably  disposed,  Madame 
Berthelot  used  to  send  all  the  cast-off  clothes  of  the 
family  to  the  cleaners,  and  after  they  had  been  carefully 
mended,  they  were  distributed  to  poor  friends. 

In  1881,  Berthelot  was  elected  a  '  Permanent  Senator ' ; 
he  thought  it  incumbent  on  him  to  bear  his  share  in  the 
government  of  his  country.  With  his  wife's  help,  he 
managed  to  carry  on  his  two  functions  at  the  same  time. 
In  his  place  in  the  Senate,  Berthelot  used  to  sit  buried  in 
his  arm-chair,  his  head  thrown  back,  and  his  eyes  closed, 
apparently  inattentive  to  all  that  passed ;  but  nothing  of 
importance  escaped  him.  He  took  a  leading  and  active 
part  as  member  of  various  Committees  dealing  with 
education,  and  in  1886,  as  Minister  of  Education  in  the 
Goblet  Cabinet,  he  busied  himself  with  the  reform  of 
educational  methods  in  such  a  manner  as  to  acquire 
a  wide  popularity;  the  Bills  introduced  by  him  dealt 
with  primary  and  with  higher  instruction,  with  universi- 
ties, and  with  technical  schools ;  in  the  last  he  was  no 
believer,  except  in  so  far  as  manual  training  was  given. 
Later,  in  1895,  he  was  for  a  short  time  Foreign  Minister 
in  the  Bourgeois  Cabinet ;  but  the  delays  of  parliamentary 
procedure  were  not  to  his  mind.  It  was  with  difficulty 
that  he  was  persuaded  to  sign  the  Anglo-French  Treaty 
denning  the  position  of  Siam ;  and,  almost  immediately 
after,  he  resigned  office. 


PIERRE  EUGENE  MARCELLIN  BERTHELOT    107 

Berthelot's  career  is  easily  told ;  it  consisted  of  honour 
after  honour.  He  was  elected  a  Member  of  the  Academic 
de  Medecine  in  1863,  and  in  1867  he  collaborated  in  the 
foundation  of  the  Ecole  des  Hautes  Etudes,  and  in  the 
reorganisation  of  scientific  teaching.  Membership  of  the 
Academic  des  Sciences  followed  in  1873,  and  in  1889  he 
became  its  Secretaire  Perpetuel. 

In  1900,  he  had  the  rare  honour  of  being  elected  among 
the  immortal  forty  in  the  Academic  Fran£aise,  succeeding 
to  the  Chair  of  Joseph  Bertrand.  Of  28  voters,  19  voted 
for  him,  9  abstaining.  Four  years  later,  in  1904,  he 
delivered  the  statutory  discourse.  He  was  a  Member  of 
the  Conseil  Superieur  des  Beaux-Arts,  of  the  Conseil 
Superieur  de  V Instruction  Publique,  and  in  1886  he  was 
created  a  Grand  Officier  of  the  Legion  of  Honour.  He 
was  Foreign  Member  of  almost  every  scientific  society 
in  the  world,  including  our  own  Royal  Society. 

On  November  24, 1901,  the  Berthelot  jubilee  celebration, 
the  anniversary  of  his  seventy-fifth  birthday,  was  held  in 
Paris,  M.  Loubet,  President  of  the  Republic,  in  the  chair. 
It  took  place  in  the  great  hall  of  the  Sorbonne ;  all  the 
Cabinet,  the  ambassadors  of  all  countries,  and  delegates 
from  universities  and  scientific  societies  from  all  over  the 
world  were  present.  Madame  Berthelot  with  her  children 
and  grandchildren  occupied  a  conspicuous  place,  beaming 
over  with  unaffected  pleasure ;  Berthelot  had  declined  the 
State  offer  to  make  a  triumphal  procession  in  the  carriage 
of  the  President  with  a  military  escort ;  he  went  on  foot 
from  the  Quai  Voltaire  to  the  Sorbonne,  his  greatcoat 
buttoned  so  as  to  hide  the  grand-cordon  of  the  Legion 
of  Honour,  and  his  head  down  so  as  to  avoid  recognition. 
He  was  embraced  by  the  President  of  the  Republic,  and 
amid  the  enthusiastic  applause  of  the  spectators,  address 
after  address  was  delivered,  each  delegate  conveying  the 
congratulations  of  the  body  which  he  represented.  It 


108    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

was  a  national  fete.  Thus  did  the  French  honour  science 
and  its  doyen. 

On  March  18,  1907,  the  end  came.  Madame  Berthelot 
had  been  ailing  for  about  three  months ;  it  turned  out  to 
be  an  attack  of  heart-disease,  dangerous  at  the  age  of 
seventy.  After  she  was  confined  to  bed,  Berthelot  watched 
by  her  each  night,  seated  in  a  deep  arm-chair,  only  leaving 
her  when  she  was  asleep.  He  himself  suffered  from  the 
same  disease,  and  it  was  accelerated  by  his  want  of  rest. 
His  family  noticed  his  feverish  appearance  in  the  morn- 
ings ;  he  excused  himself  by  saying  that  he  was  finishing 
a  memoir  for  publication.  On  Passion  Sunday  there  was 
a  slight  improvement,  and  Berthelot  passed  the  afternoon 
in  his  laboratory  at  Meudon.  That  night,  however, 
Madame  Berthelot  became  comatose,  and  her  husband 
never  left  her  bedside  until  Monday  at  four,  when  the  end 
came.  Berthelot  suddenly  rose  from  the  arm-chair  in 
which  he  was  seated,  threw  his  arms  in  the  air,  uttered  a 
cry,  and  fell  back  dead.  They  died,  as  they  had  lived, 
together. 

It  now  remains  to  give  a  sketch  of  Berthelot's  scientific 
work.  The  '  Prix- Jecker '  has  already  been  alluded  to. 
This  was  the  reward  of  his  labours  on  the  synthesis  of 
carbon  compounds.  He  began  in  1851  by  investigating 
the  action  of  a  red-heat  on  alcohol,  acetic  acid,  naphtha- 
lene, and  benzene ;  this  led  him  in  1860  to  the  rediscovery 
of  acetylene,  a  compound  originally  obtained  by  Edmund 
Davy,  Sir  Humphry's  brother.  In  1856  he  synthesised 
methane  by  the  action  of  a  mixture  of  sulphuretted 
hydrogen  with  carbon  disulphide  on  copper ;  and  in  1862 
he  obtained  ethylene  and  acetylene  by  heating  marsh-gas 
to  redness.  His  condensation  of  acetylene  to  benzene  in 
1866  established  the  first  link  between  the  fatty  and  the 
aromatic  series.  His  direct  synthesis  of  acetylene  from 
carbon  and  hydrogen  in  1862,  and  the  formation  of  alcohol 


PIERRE  EUGJBNE  MARCELLIN  BERTHELOT    109 

by  hydrolysing  ethyl- sulphuric  acid,  obtained  by  absorbing 
ethylene  in  sulphuric  acid,  taken  in  conjunction  with  his 
synthesis  of  hydrocyanic  acid  in  1868,  pointed  the  way  to 
the  formation  from  the  elements  of  innumerable  com- 
plicated compounds  of  carbon. 

Much  light  has  also  been  thrown  by  Berthelot  on  the 
alcohols.  In  1857  he  produced  methyl  alcohol  from 
marsh-gas  by  chlorination  and  hydrolysis;  in  1858  he 
recognised  eholesterine,  trehalose,  meconine,  and  camphol 
as  alcohols ;  in  1863  he  added  thymol,  phenol,  and  cresol 
to  the  same  class ;  and  he  showed  how  to  diagnose  alcohols 
by  acetylation. 

Turning  to  the  esters,  the  nature  of  glycerine  occupied 
his  attention  in  1853 ;  in  that  year  he  succeeded  in  syn- 
thesising  some  animal  fats,  and  showing  their  analogy 
with  esters,  as  has  already  been  mentioned ;  and  he  pre- 
pared other  salts  of  glyceryl  by  submitting  it  to  the  action 
of  acids.  The  action  of  hydriodic  acid  was,  however, 
found  to  yield  two  substances  of  a  different  nature,  namely 
isopropyl  iodide,  and  allyl  iodide ;  and  from  the  latter  he 
prepared,  for  the  first  time,  artificial  oil  of  mustard.  The 
analogy  of  sugars  with  glycerine  led  him  to  investigate 
the  action  of  acids  on  sugars,  and  this  resulted  in  the 
synthesis  of  many  of  their  esters.  The  fermentation  of 
mannite  and  other  polyhydric  alcohols  was  also  studied 
in  1856  and  1857,  also  the  conversion  of  mannite  and 
glycerine  into  sugars,  properly  so  called.  The  esters  of 
pinite,  etc.,  with  tartaric  acid,  were  also  studied,  and  in 
1858,  trehalose  and  melezitose  were  discovered.  In  1859, 
Berthelot  maintained  that  the  action  of  yeast  is  not  a  vital, 
but  a  chemical  phenomenon ;  and  he  returned  again  and 
again  to  the  study  of  fermentation. 

These  and  other  similar  investigations  on  esters  led  him, 
in  conjunction  with  Pean  de  Saint- Gilles,  to  investigate 
the  rate  of  esterification  ;  and  the  experiments,  begun  in 


110    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

1861,  led  to  a  long  piece  of  work  on  chemical  equilibrium, 
and  on  'affinity.'  In  1869  he  attempted  to  limit  the 
action  of  hydrochloric  acid  on  zinc  by  pressure,  but  unsuc- 
cessfully ;  and  in  the  same  year  he  investigated  the 
equilibrium  between  carbon  and  hydrogen,  in  sparking 
acetylene  under  pressure.  And  later  in  that  year  he 
announced  laws,  describing  the  partition  of  bodies  between 
two  solvents,  and  he  investigated  the  state  of  equilibrium 
in  solution.  In  the  same  year  appeared  the  first  of  the 
long  series  of  researches  on  thermal  chemistry.  In  18*75 
he  returned  to  the  subject  of  chemical  equilibrium,  deal- 
ing with  the  partition  of  acids  between  several  bases  in 
solution. 

Among  other  syntheses  was  that  of  formic  acid  from 
caustic  soda  and  carbon  monoxide ;  oxalic  acid  was  pro- 
duced by  the  oxidation  of  acetylene ;  and  acetates,  by  the 
slow  oxidation  of  acetylene,  in  contact  with  air  and 
caustic  potash,  in  diffuse  daylight. 

In  1857  the  combination  of  unsaturated  hydrocarbons 
with  the  halogen  acids  was  studied,  as  well  as  the  conver- 
sion of  chloro-  and  bromo-hydrocarbons  into  hydrocarbons 
by  reduction.  In  1860  ethyl  iodide  was  synthesised  by 
the  union  of  ethylene  with  hydriodic  acid;  and  in  1867 
the  use  of  a  concentrated  solution  of  hydriodic  acid  as  a 
universal  reducing  agent  at  high  temperatures  was  dis- 
covered. 

Berth elot's  numerous  and  important  researches  on  the 
acetylides  of  silver  and  copper  doubtless  led  him  to  pay 
attention  to  explosives.  Begun  in  1862,  they  were  con- 
tinued until  1866  ;  and  in  that  year  he  enunciated  the 
theory  that  the  production  of  mineral  oils  may  conceivably 
have  been  due  to  the  action  of  water  and  carbonic  acid  on 
acetylides  of  the  alkaline  metals,  and  to  the  subsequent 
resolutions  of  acetylene  at  a  high  temperature  into  other 
hydrocarbons.  These  researches  on  the  acetylides  were 


PIERRE  EUGENE  MARCELLIN  BERTHELOT    111 

followed  in  1870  by  investigations  on  the  explosive  force 
of  powders,  the  explosions  being  carried  out  in  a  calori- 
meter. 

In  1871  Berthelot  proceeded  to  investigate  the  detona- 
tion of  mixtures  of  gases,  and  he  made  measurements  of 
the  heat  of  formation  of  nitro-glycerine.  In  1874  and 
1876  the  work  was  continued ;  and  in  1877  it  was  extended 
to  the  temperatures  of  explosive  mixtures,  and  to  the 
velocity  of  combustion.  In  1878  explosive  mixtures  of 
dust  with  air,  and  in  1880  fulminating  mercury,  were 
examined.  A  research  on  the  velocity  of  the  explosive 
wave  in  gases  followed  in  1882 ;  and  in  1884  measure- 
ments of  the  specific  heats  of  gases  at  high  temperatures 
were  made.  In  the  same  year  the  calorimetric  bomb  was 
invented ;  and  in  1892  it  was  adapted  to  the  requirements 
of  organic  analysis. 

Allotropic  varieties  of  the  elements  also  claimed  Ber- 
thelot's  attention.  In  1857  he  commenced  with  a  study 
of  allotropic  varieties  of  sulphur ;  and  in  1870  he  investi- 
gated these  varieties  thermally.  In  1869  he  examined 
the  allotropic  varieties  of  carbon,  and  this  led  him  to  the 
preparation  of  various  forms  of  graphitic  oxides.  Allo- 
tropic silver  and  other  allotropic  forms  were  also  the 
subject  of  his  research. 

Berthelot  also  did  much  work  by  help  of  the  'silent 
discharge.'  Attracted  to  it  in  1876,  when  he  submitted 
mixtures  of  organic  substances  with  nitrogen  to  its 
influence,  and  succeeded  in  causing  the  nitrogen  to  enter 
into  combination,  he  repeated  Brodie's  experiments,  and 
reproduced  the  oxide  C404.  In  1878  he  produced  by  the 
same  means  the  higher  oxide  of  sulphur,  S207,  in  needles 
often  a  centimetre  in  length,  and  in  1881  pernitric 
anhydride.  In  1895  he  carried  out  similar  work  with 
argon,  and  later  with  helium. 

From   an   early  date   Berthelot  interested  himself  in 


112    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

agricultural  chemistry.  From  his  laboratory  at  Meudon, 
assisted  by  his  colleague,  Andre,  have  appeared  a  succes- 
sion of  memoirs,  chiefly  relating  to  the  absorption  of 
nitrogen  by  plants,  and  to  their  behaviour  under  the 
influence  of  electric  energy.  To  the  very  end  his  interest 
was  kept  up  in  these  experiments ;  and  he  was  hopeful  of 
increasing  by  electrical  means  the  productiveness  of 
cereals,  and  of  adding  to  the  world's  food-supply. 

Though  so  keenly  alive  to  the  present,  the  past  had  for 
Berthelot  a  great  attraction.  In  1877  he  analysed  a 
sample  of  Roman  wine,  which  had  been  preserved  in  a 
sealed  flask ;  and  he  has  contributed  to  the  Journals  many 
notices  of  the  composition  of  ancient  objects  of  metal. 
His  works  on  Les  Origines  de  VAlchimie,  and  on  a  Collec- 
tion des  anciens  Alchimistes  grecs,  texte  et  traduction,  and 
his  Introduction  d  I' etude  de  la  Chimie  des  Anciens  et  du 
moyen  dge,'  involved  long  research  of  ancient  manuscripts ; 
he  acquired  facility  in  reading  ancient  Greek,  though  for 
Arabian  sources  he  was  dependent  on  others. 

Berthelot  was  the  author  of  numerous  works  besides 
those  on  Alchemy.  In  1872  he  published  a  Treatise  on 
Organic  Chemistry;  a  fourth  edition  appeared  in  1899. 
This  was  followed  by  La  Synthese  chimique  ;  Essai  de 
Chimie  mechanique  (1879),  in  which  he  announced  the 
principle  of  '  maximum  work,'  a  doctrine  afterwards  with- 
drawn, or,  at  least,  greatly  modified  in  1894;  Traite 
2^ratique  de  Calorimetrie  chimique  (1893);  Thermochimie : 
Donnees  et  lois  numeriques  (1898),  in  which  an  account 
of  his  long  series  of  calorimetrical  measurements  is 
given ;  this  work  and  that  of  Julius  Thomsen  on  Ther- 
.mochimie  are  the  standard  books  on  the  subject,  and 
each  contains  the  results  of  the  individual  researches  of 
its  author. 

Berthelot's  mind  was  one  which  interested  itself  greatly, 
not  merely  with  things,  but  with  their  origins;  and  in 


PIERRE  EUGfeNE  MARCELLIN  BERTHELOT    113 

Science  et  Philosopliie  and  Science  et  Morale  he  treats  of 
the  relation  of  science  to  human  thought.  The  same 
critical  spirit  manifests  itself  in  his  Histoire  des  Sciences : 
La  Chimie  au  moyen  age,  in  which  Syrian  and  Arabian 
Alchemy  is  treated  of. 

A  partisan  of  Lavoisier,  La  Revolution  chimique  de 
Lavoisier  presents  that  point  of  view  strongly.  He  also 
published  in  1898  his  correspondence  with  Renan. 

The  lectures  which  he  delivered  at  the  College  de 
France  were  published  under  the  titles  Lecons  sur  les 
Methodes  generates  de  Synthese  en  Chimie  organique ; 
Lemons  sur  la  thermochimie ;  Lecons  sur  les  principes 
sucres ;  and  Lecons  sur  I'isomerie.  The  application  of 
thermal  chemistry  to  problems  of  life  was  treated  of  in 
his  Chaleur  animate,  and  in  1901  he  published  three 
volumes  on  Les  Carbures  d'Hydrogene. 

One  point  remains  to  be  mentioned.  It  has  sometimes 
been  objected  that  Berthelot  kept  science  on  a  wrong 
path  by  persistently  retaining  the  old  system  of  represent- 
ing formulae,  after  all  the  rest  of  the  world  had  aban- 
doned it.  The  writer  remembers  well  a  conversation  in 
the  late  '80's,  in  which  Berthelot  defended  his  views.  He 
thought  the  position  of  those  who  employed  the  customary 
notation  (and,  of  course,  they  comprised  practically  the 
whole  chemical  world)  not  unlike  that  of  the  defenders  of 
the  phlogiston  theory !  The  retort  was  obvious,  but  not 
made.  Berthelot  had  not  even  the  excuse  of  Cavendish, 
who,  after  a  calm,  deliberate  statement  of  the  results  of 
his  research  in  terms  of  the  then  new  hypothesis  of 
Lavoisier,  restated  it  in  terms  of  the  phlogistic  method, 
saying  that  he  preferred  to  make  use  of  the  older  and 
better  known  language,  rather  than  of  the  newer  modes 
of  expression.  For  in  1890  Berthelot  was,  perhaps,  the 
only  survivor  of  the  older  chemists.  Professor  Guye,  who 
attended  his  lectures  in  1890-91,  tells  that  the  session  was 

H 


114    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

begun,  as  usual,  with  the  special  notation  of  which  Ber- 
thelot  was  the  sole  defender  ('  equivalents  based  on  two 
volumes  of  vapour '),  and  that,  without  the  slightest  warn- 
ing in  the  middle  of  a  chapitre,  to  the  great  astonishment  of 
his  audience,  he  effected  the  change,  dealing  with  a  subject 
of  which  the  first  portion  had  been  expounded  in  the 
'  equivalent '  notation,  and  continuing  in  the  newer  nota- 
tion of  which  he  had  so  long  been  the  opponent. 

No  one  is  more  conscious  than  the  writer  that  he  has 
failed  to  do  justice  to  this  remarkable  personality.  His 
only  excuse  is  that  he  has  done  his  best.  He  wishes  that 
it  were  possible  to  convey  to  the  reader  a  sense  of  the 
brilliancy,  the  vivacity,  the  power,  the  ability,  the  talent, 
and  the  high  character  of  the  great  chemist.  In  the  life- 
like plaquette  by  Chaplain,  his  features  and  his  attitude 
have  been  admirably  reproduced.  Truly  he  was  one  of 
the  most  remarkable  of  the  eminent  men  of  whom  France 
may  be  proud.  He  and  his  wife  lie  in  the  vaults  of  the 
Pantheon,  in  life  united,  in  death  not  put  asunder. 


II.   CHEMICAL  ESSAYS 

HOW  DISCOVERIES  ARE  MADE 

THERE  is  a  difference  between  discovery  and  invention. 
A  discovery  brings  to  light  what  existed  before,  but  what 
was  not  known ;  an  invention  is  the  contrivance  of  some- 
thing that  did  not  exist  before.  I  suppose,  however,  that 
inventions  and  discoveries  are  made  in  much  the  same 
manner ;  though  I  have  no  claim  to  speak  as  an  inventor, 
except  in  a  very  small  way. 

Many  people,  probably  most  people,  think  that  when  a 
discovery  is  made,  it  comes  all  in  a  flash,  as  it  were — that 
a  new  idea  suddenly  crops  up,  and  its  conception  is  a  dis- 
covery. That  may  sometimes  be  the  case. 

We  have  all  heard  of  the  puzzle  given  to  Archimedes ; 
how  he  was  asked  to  find  out,  without  injuring  it  in  the 
least,  whether  a  certain  crown  consisted  of  silver  or  of 
gold ;  and  by  weighing  it  in  air  and  in  water,  he  invented 
the  method  of  taking  specific  gravity;  for  the  crown  when 
weighed  in  water  lost  weight  equal  to  that  of  the  water 
which  it  displaced.  And  he  ran  through  the  streets  of 
Alexandria,  crying, '  Heureka !  I  have  found  it ! ' 

His  finding  that  the  crown  was  of  gold  was  a  discovery ; 
but  he  invented  the  method  of  determining  the  density  of 
solids.  Indeed,  discoverers  must  generally  be  inventors ; 
though  inventors  are  not  necessarily  discoverers. 

116 


116    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

It  is  too  often  supposed  that,  like  the  poet,  discoverers 
are  '  born,  not  made  ' ;  but  I  think  I  shall  be  able  to  show 
that  many  people,  though  not  all,  have  in  them  the  power 
of  making  discoveries ;  and  if  this  short  article  can  give 
to  any  one  the  hope  of  making  discoveries,  and  prompt 
him  to  try,  it  will  have  more  than  achieved  its  object. 

Like  every  other  endeavour,  the  beginning  is  in  small 
things.  Any  one  who  tries  to  look  into  anything  with 
sufficient  care  will  find  something  new.  A  drop  of  water ; 
a  grain  of  sand ;  an  insect ;  a  blade  of  grass ;  we  know  in- 
deed little  about  them  when  all  is  told.  First,  of  course, 
we  must  learn  what  others  have  done ;  and  for  that  pur- 
pose we  go  to  school  and  to  college,  and  read  books  and 
hear  lectures.  Before  beginning,  we  should  at  least  have 
an  idea  of  what  has  been  achieved  by  our  predecessors. 
After  that  there  is  nothing  for  it  but  to  try. 

But  there  are  two  ways  of  trying :  and  Avhat  I  wish  to 
convey  is  best  told  in  an  allegory. 

There  are  two  kinds  of  fishers :  those  who  fish  for 
sprats  and  those  who  angle  for  salmon.  I  do  not  say 
there  are  not  others ;  but  these  two  kinds  are  at  the 
extremes  of  the  fishing  world.  The  fishers  for  sprats  are 
sure  of  a  large  catch,  or  at  least  of  catching  something ; 
but  the  fish  are  small,  not  particularly  attractive  as  food, 
and  of  no  great  value ;  they  are,  however,  numerous  and 
easily  caught.  But  the  salmon  fisher  hunts  a  very  dif- 
ferent prey ;  if  there  is  any  special  quality  about  a  salmon, 
it  is  his  power  of  motion  and  his  fickleness  of  taste ;  so 
that  the  angler,  when  he  casts  his  line,  is  by  no  means 
sure  that  a  fish  is  within  reach  of  his  cast,  nor,  if  he  is, 
whether  he  will  rise  to  the  fly.  If  fate  is  propitious,  how- 
ever, his  prize  is  a  great  one;  his  pleasure  consists  not 
merely  in  catching  the  fish,  but  in  struggling  with  him, 
possibly  for  an  hour  or  more ;  wading  after  him  in  alter- 
nate hope  and  fear — hope  that  his  line  may  stand  the 


HOW  DISCOVERIES  ARE  MADE  117 

strain,  fear  that  it  may  part,  or  that  some  hasty  move- 
ment may  lose  him  his  fish. 

Most  discoverers  are  like  fishers  for  sprats :  they  go 
where  they  are  sure  of  a  reward ;  but  the  gain  is  not 
great,  at  least  as  regards  sport.  It  is  much  more  fun  to 
fish  for  salmon ;  but  then  there  is  a  great  chance  that  the 
angler  has  mistaken  the  place  to  fish,  or  that  he  has  used 
the  wrong  fly ;  or  that  the  weather  is  unfavourable ;  or 
that  a  hundred  things,  impossible  to  foresee,  will  prevent 
the  salmon  taking  the  hook. 

We  may  not  pursue  the  allegory  further:  salmon  are 
now  not  nearly  so  plentiful  a$  they  used  to  be;  sprats, 
perhaps  even  more  numerous.  And  it  requires  training 
and  a  good  eye  to  know  where  the  salmon  lie  and  in  what 
pools  to  fish. 

But  let  us  dismiss  this  image  and  become  historical. 

One  of  the  first  puzzles  which  awaited  solution  was  the 
nature  of  flame.  The  ancients  believed  it  to  be  an  ele- 
ment— that  is,  a  property,  or  perhaps  a  constituent  of 
most,  or  of  all,  other  things.  Flame,  said  they,  is  hot; 
and  everything  which  is  hot  partakes  of  the  nature  of 
flame. 

Robert  Boyle  guessed  that  it  was  a  sign  of  the  rapid 
movement  of  the  minute  particles  of  which  he  supposed 
everything  to  be  composed ;  but  this,  although  very  near 
what  we  now  suppose  to  be  the  truth,  was  merely  a  lucky 
guess ;  for  he  had  no  real  ground  for  making  the  sugges- 
tion. It  was  noticed  that  flame  appears  when  anything 
burns;  and  the  reason  for  combustion,  or  burning,  had 
first  to  be  sought. 

The  real  step  towards  this  was  made  by  Joseph  Priestley, 
an  English  dissenting  minister,  and  by  Karl  Scheele,  a 
Swedish  apothecary,  almost  at  the  same  time.  Priestley 
was  a  fisher  for  salmon,  to  revert  to  our  old  image ;  he 
fished  everywhere  and  caught  many  large  fish.  And  so 


\ 


118    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

was  Scheele.  They  noticed  that  when  certain  substances 
were  heated,  gases — or,  as  they  termed  them,  'airs' — escape. 
For  it  had  been  supposed  that  all  gases,  as  we  now  name 
them,  were  merely  modifications  of  ordinary  air ;  just  as 
we  sometimes  notice  a  pleasant  or  a  disagreeable  smell, 
and  attribute  it  to  the  '  goodness '  or '  badness '  of  the  air,  so 
it  was  generally  thought  that  gases,  such  as  coal-gas,  were 
a  sort  of  air  with  an  unpleasant  odour  and  the  curious 
property  of  catching  fire. 

About  fifteen  years  before  Priestley  and  Scheele  made 
their  great  discovery  of  oxygen,  the  constituent  of  air 
which  supports  combustion,  a  Scottish  professor,  Joseph 
Black,  investigated  the  particular  kind  of  'air'  which 
escapes  when  chalk  or  limestone  is  heated.  And  he  made 
the  great  discovery  that  this  '  air '  can  be  reabsorbed  by 
lime — the  residue  left  after  chalk  is  heated  —  so  that 
chalk  is  again  formed. 

Moreover,  he  weighed  the  chalk  before  it  was  heated, 
he  measured  the  gas,  and  he  weighed  the  lime  left  after 
the  gas  had  been  driven  off  from  the  chalk.  And  lastly 
he  weighed  the  chalk  which  was  re-formed  after  the  lime 
had  absorbed  the  gas. 

He  found  that  the  lime  was  lighter  by  just  as  much 
as  the  gas  weighed ;  and  he  called  this  gas  '  fixed  air/  to 
emphasise  the  fact  that  it  could  be  '  fixed '  or  absorbed  by 
lime  and  similar  substances. 

This  first  opened  the  way  for  the  investigation  of  gases  ; 
it  was  a  great  discovery — perhaps  one  of  the  most  fertile 
which  has  ever  been  made.  It  is  to  be  noted  that  Black 
was  not  content  with  this,  however;  for  he  recognised 
that  the  fixed  air  from  chalk  was  of  the  same  nature  as 
steam  from  water.  And  just  as  it  was  necessary  to  heat 
water  so  as  to  drive  it  into  steam,  so  it  appeared  to  him 
that  carbonic  acid  gas,  to  give  '  fixed  air '  a  more  modern 
name,  was  a  gas  by  virtue  of  the  heat  or  '  caloric '  which  it 


HOW  DISCOVERIES  ARE  MADE  119 

contained.  He  went  on  to  discover  how  much  heat  is 
required  to  convert  a  known  weight  of  water  into  steam. 
He  found  that  about  fifty-four  times  as  much  heat  is 
required  as  is  necessary  to  heat  the  same  weight  of  water 
from  the  freezing-point  to  the  boiling-point.  But  the 
steam  is  no  hotter  than  the  boiling  water ;  hence  Black 
called  this  heat  the  '  latent  heat '  of  steam,  because  it  lies 
hidden  in  the  steam  and  does  not  affect  a  thermometer. 
Black  made  quantitative  experiments  —  that  is,  he  not 
merely  made  discoveries,  but  found  the  quantities  in 
which  the  changes  took  place. 

The  way  was  now  plain  for  Priestley  and  Scheele.  They 
heated  all  kinds  of  substances  :  if  they  evolved  gas,  that 
gas  was  collected  and  examined ;  but  neither  Priestley  nor 
Scheele  paid  much  attention  to  quantities.  The  methods 
of  dealing  with  gases  had  to  be  invented,  moreover.  And 
while  Scheele  caught  his  gases  in  bladders,  Priestley  in- 
vented, or  rather  reinvented,  what  he  called  a  '  pneumatic 
trough,'  a  vessel  filled  with  water  containing  jars  and 
bottles  standing  inverted  full  of  water.  If  the  tube  lead- 
ing from  the  retort  in  which  the  substance  evolving  the 
gas  was  heated  was  directed  so  that  its  open  end  was 
directly  under  the  mouth  of  the  bottle,  the  escaping  gas 
entered  the  bottle  and  displaced  the  water ;  and  when  the 
bottle  was  full,  it  could  be  corked,  still  under  water,  and 
removed  so  that  the  gas  could  be  examined. 

It  is  usually  the  case  that  discoveries  have  to  be  accom- 
panied by  inventions;  the  sequence  is  that  to  try  any 
new  thing,  a  piece  of  apparatus  has  to  be  devised  which 
will  effect  the  purpose — or  perhaps  an  apparatus  already 
known  has  to  be  altered — so  that  it  may  almost  be  said 
that  invention  and  discovery  go  hand  in  hand. 

For  this  reason  it  is  very  important  that  the  discoverer 
should  be  a  good  worker  in  all  kinds  of  materials — in  glass, 
for  most  small  pieces  of  apparatus  can  best  be  constructed 


120    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

of  glass :  in  brass,  for  if  anything  of  the  nature  of  machinery, 
such  as  pumps,  stirrers,  etc.,  is  required,  brass  is  perhaps 
the  most  convenient  material;  in  clay,  for  vessels  are 
wanted  which  will  withstand  a  high  temperature ;  and  of 
recent  years  silica  glass,  made  from  fused  rock-crystal,  has 
proved  of  great  use,  for  it  can  be  worked  before  a  blow-pipe 
fed  with  coal-gas  and  oxygen. 

But  to  return  to  the  discovery  of  oxygen.  Priestley 
heated  oxide  of  mercury,  or,  as  he  called  it, '  red  precipi- 
tate,'in  a  retort,  and  collected  the  escaping  gas;  and  he 
found  that  a  candle  burned  in  it  much  more  brightly  than 
in  air;  and,  moreover,  after  having  found  that  a  mouse 
could  live  in  it  longer  than  in  the  same  volume  of  air, 
confined  in  a  bottle,  he  breathed  it  himself  and  found 
that  its  effect  was  pleasant  and  exhilarating. 

Similar  experiments  were  made  by  Scheele  with  the 
same  result;  but  Scheele  went  much  further.  Having 
noticed  that  a  number  of  substances  had  the  property  of 
making  combustible  bodies,  such  as  wood,  flour,  and 
charcoal,  deflagrate,  or  burn  more  brilliantly  when  mixed 
with  them,  he  heated  these  substances,  and  found  that 
they  too  evolved  oxygen  gas.  Among  the  substances 
were  red-lead,  black  oxide  of  manganese,  nitre,  and  many 
others ;  so  he  established  a  general  rule  that  those  sub- 
stances which  can  be  mixed  with  charcoal  to  make  a  kind 
of  gunpowder  will  evolve  oxygen  when  heated. 

It  thus  became  known  that  air  contained  a  gas,  amount- 
ing to  about  a  fifth — Scheele  says  a  sixth — of  its  bulk, 
possessing  the  property  of  making  combustible  objects 
burn  with  greater  vigour.  Flame,  therefore,  was  caused 
by  the  action  of  oxygen,  as  the  new  gas  was  called  later, 
with  combustible  bodies. 

It  would  take  too  long  to  consider  the  curious  doctrine 
of  'phlogiston,'  an  immaterial  effluvium  which  was  sup- 
posed to  escape  when  bodies  burn ;  I  can  merely  mention 


HOW  DISCOVERIES  ARE  MADE  121 

that  Lavoisier,  a  celebrated  French  chemist,  gave  the 
correct  explanation  of  combustion — namely,  that  it  is 
caused  by  the  union  of  oxygen  with  the  substance  burning. 
Lavoisier,  however,  cannot  be  ranked  as  a  great  discoverer, 
though  he  shone  as  an  interpreter  of  the  discoveries  of 
others. 

Henry  Cavendish,  who  did  his  best  work  between  1770 
and  1790,  discovered  the  composition  of  water ;  that  it  is 
produced  when  oxygen  and  hydrogen  unite;  and  he 
determined  with  great  accuracy  the  proportions  by  volume 
in  which  the  union  of  the  two  gases  is  completed.  He 
also  attempted  to  show,  by  passing  electric  sparks  through 
a  mixture  of  the  inert  gas  of  the  atmosphere,  nitrogen, 
mixed  with  oxygen,  that  nitrogen  was  a  single  substance 
and  not  a  mixture ;  nearly  all  the  nitrogen  disappeared 
under  this  treatment,  only  about  one  hundred-and- 
twenty-fifth  of  the  whole  being  left.  It  would  hardly 
have  been  possible  for  him,  in  the  existing  state  of  know- 
ledge, with  the  imperfect  appliances  which  alone  were 
available  at  that  time,  to  have  identified  his  inactive 
residue  with  'argon/  a  gas  discovered  more  than  a 
century  later;  for  the  spectroscope  was  then  unknown, 
and  it  is  the  chief  means  of  identifying  and  characterising 
gases,  and  indeed  elements  of  every  kind.  This  is  an 
example  of  how  discovery  has  sometimes  to  wait  on  in- 
vention ;  for,  until  the  instruments  of  research  are  invented, 
it  is  almost  impossible  to  confirm  a  discovery,  even 
although  it  may  be  genuine. 

The  true  nature  of  flame,  which,  as  before  remarked, 
has  been  a  puzzle  since  the  remotest  ages,  has  had  to 
wait  on  invention  for  its  discovery.  When  a  current  of 
electricity  of  high  tension,  such  as  is  produced  by  an 
induction-coil  or  by  an  electric  machine,  is  passed  through 
any  rarefied  gas,  it  gives  out  a  peculiar  and  often  a  very 
beautiful  coloured  light :  sometimes  red,  as  in  the  case  of 


122    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

hydrogen  or  neon;  sometimes  bluish-white,  as  with 
carbonic  acid  or  krypton ;  sometimes  purple-red,  as  with 
argon  or  nitrogen.  When  examined  through  a  prism  or 
a  spectroscope,  this  light  is  seen  to  consist  of  a  number  of 
colours,  which  blend  to  give  the  colour  seen  with  the 
naked  eye. 

Thus  the  brilliantly  red  spectrum  of  hydrogen  is  easily 
shown  to  be  a  compound  impression ;  the  red  light,  which 
is  the  brightest,  is  mixed  with  and  slightly  modified  by 
a  blue- green  and  a  violet  light.  Tubes  which  are  well 
adapted  to  show  this  light  were  invented  by  a  German 
physicist  named  Plticker  in  the  'fifties.  Twenty-five 
years  later,  Sir  William  Crookes,  with  the  aid  of  his 
skilful  assistant,  Mr.  Gimingham,  improved  the  then 
existing  form  of  air-pump,  invented  by  Dr.  Hermann 
Sprengel,  so  that  it  became  capable  of  exhausting  the 
air  much  more  completely  than  was  previously  pos- 
sible. 

He  found  that,  at  a  much  greater  exhaustion  than  that 
which  causes  gases  to  glow  and  give  out  their  spectrum,  a 
current  of  high-tension  electricity  produced  in  the  tube  a 
violet  or  a  green  phosphorescence,  according  as  the  glass 
of  which  it  was  made  contained  lead  and  potash,  or  lime 
and  soda,  combined  with  the  silica,  or  sand. 

Moreover,  the  position  of  this  curious  phosphorescent 
glow  depended  on  the  shape  and  direction  of  the  wire  or 
plate  from  which  the  negative  electricity  passed  into  the 
tube.  From  a  wire  the  glow  proceeded  in  all  directions 
perpendicular  with  its  length,  so  as  to  colour  the  tubes 
immediately  surrounding  the  wire  with  phosphorescent 
light.  If  the  wire,  however,  were  terminated  with  a  plate, 
then  the  phosphorescent  light  appeared  mostly  between 
the  front  of  the  plate  and  the  positive  wire  of  the  vacuum- 
tube.  Supposing  the  plate  were  curved,  so  as  to  form  a 
concave  metallic  reflector,  the  light  of  what  was  evidently 


HOW  DISCOVERIES  ARE  MADE  123 

a  discharge  was  concentrated  on  a  point  at  the  focus  of 
the  metallic  mirror. 

Moreover,  if  an  object  of  any  kind  were  placed  at  the 
focus,  and  submitted  to  the  discharge,  it  became  intensely 
hot;  or  if  it  could  move — if,  for  instance,  it  formed  the 
vanes  of  a  little  wheel  or  windmill — the  wheel  revolved 
rapidly  as  if  it  were  being  bombarded  by  infinitesimally 
small  bullets.  Crookes  imagined  that  by  being  thus 
highly  rarefied,  the  gaseous  matter  changed  so  as  to 
become  '  ultra-gaseous,'  that  it  changed  its  state  in  some- 
what the  same  manner  as  ice  becomes  water  or  as  water 
becomes  steam. 

It  is  interesting  here  to  recall  how  Sir  William  Crookes 
came  to  make  these  most  remarkable  discoveries.  He 
began  by  using  a  spectroscope  to  investigate  the  spectrum 
or  coloured  light  given  out  by  the  various  constituents 
into  which  he  had  analysed  the  dust  which  deposits  in 
the  flues  used  to  convey  the  sulphurous  acid  produced  by 
the  burning  of  pyrites  (a  compound  of  sulphur  and  iron), 
then  (in  the  'sixties)  recently  introduced  as  a  source  of 
sulphur  for  the  manufacture  of  sulphuric  acid  or  oil  of 
vitriol.  One  of  his  precipitates,  when  examined  with  the 
spectroscope,  showed  the  presence  of  a  bright  green  light ; 
and  this  was  traced  to  the  presence  of  a  new  element,  to 
which  he  gave  the  name  'thallium,'  from  the  Greek 
thallos,  a  green  twig. 

One  of  the  first  things  done  with  a  new  element  is  to 
try  to  discover  its  '  equivalent' — that  is,  the  proportion  by 
weight  of  the  element  which  will  combine  with  8  parts 
by  weight  of  oxygen.  (The  number  8  is  chosen,  because 
8  parts  by  weight  of  oxygen  combine  with  1  part  of 
hydrogen  to  form  water.)  The  weighings  require  to  be 
very  accurately  made;  and  a  peculiarity  which  affects  all 
attempts  to  weigh  very  accurately  must  now  be  told  of. 
The  question  is  often  asked  as  a  catch : — '  Which  weighs 


124    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

most :  a  pound  of  feathers  or  a  pound  of  lead  ? '  The 
usual  answer  is, '  They  weigh  the  same.' 

Although  this  is  strictly  true  (for  a  pound  is  a  pound, 
whether  of  lead  or  feathers),  a  little  consideration  will 
show  that  when  the  feathers  are  placed  on  one  pan  of  a 
pair  of  scales  and  the  lead  on  the  other,  the  lead  takes  up 
far  less  room  than  the  feathers;  in  other  words,  the 
feathers  displace  much  air,  while  the  lead  displaces  little. 
That  is,  the  air  which  the  feathers  displace  no  longer 
rests  on  the  pan ;  and  if  it  were  still  there,  the  feathers 
would  weigh  more.  Hence  a  so-called  pound  of  feathers 
weighs  less  than  it  ought  to  by  the  weight  of  the  air 
displaced. 

Now  to  overcome  this  difficulty  and  to  avoid  the  some- 
what complicated  and  uncertain  calculations  necessary  to 
ascertain  the  true  weight  of  the  things  weighed,  Sir 
William  Crookes  devised  a  balance  closed  in  by  a  case  in 
which  a  vacuum  could  be  made.  And  it  was  while 
obtaining  this  vacuum  that  he  discovered  that  light 
apparently  (but  really  heat)  appears  to  repel  certain 
objects  more  than  others.  Thus  he  was  led  to  experi- 
ment on  vacuum-tubes  and  to  perform  all  the  beautiful 
experiments  which  have  made  his  name  so  famous.  At 
the  same  time  he  invented  the  '  radiometer,'  a  pretty  little 
toy  for  showing  the  repelling  action  of  heat. 

Here  again  we  see  the  advantage  of  following  up  small 
trails;  they  may  widen  to  great  and  most  important 
roads.  If  Sir  William  had  been  content  to  weigh  his 
compounds  of  thallium  in  his  vacuum-balance,  as  most 
others  would  have  done,  and  had  not  had  the  genius  to 
follow  this  side-track,  he  would  have  missed  many  of  his 
greatest  discoveries. 

A  further  great  step  was  made  when  the  German 
physicist  Lenard  found  that  Crookes's  '  rays ' — the  '  fourth 
form  of  matter '  which  he  supposed  to  be  repelled  from 


HOW  DISCOVERIES  ARE  MADE  125 

the  negative  pole  of  the  Plucker  tube  when  very  highly 
exhausted — could  pass  out  of  the  tube  through  a  thin 
1  window '  of  the  very  light  and  strong  metal  aluminium. 
It  is  true  they  could  not  pass  very  far ;  they  soon  became 
scattered.  Here  was  a  discovery  made  with  a  set  purpose. 
Professor  Lenard  wished  to  decide  the  question  whether 
Crookes's  '  rays '  were  really  due  to  a  stream  of  corpuscles 
or  whether  they  were  vibrations  like  those  of  light. 

Sir  William  had  previously  found  that  if  a  magnet  were 
placed  near  the  tube  the  path  of  the  rays  was  no  longer 
straight,  but  curved.  And  Lenard  observed  that  if  the 
aluminium  window  were  placed  so  that  a  '  vacuum '  (not 
a  complete,  but  a  nearly  complete  one)  were  on  both  sides  of 
the  aluminium  window,  the  'rays'  could  be  bent  out  of  their 
course  by  the  magnet  after  passing  through  the  window. 

It  must  be  remembered  that  these  rays  are  not  them- 
selves visible ;  it  is  only  possible  to  see  where  they  strike 
by  their  causing  phosphorescence.  Professor  Rontgen, 
the  celebrated  German  physicist,  discovered  in  his  turn 
that  if  these  rays  be  suddenly  stopped — say  by  falling  on 
glass  or  metal — rays  of  another  kind  are  sent  on,  which 
have  the  power  of  affecting  a  photographic  plate  and  of 
rendering  certain  substances  exposed  to  them  phosphores- 
cent; so  that,  as  different  kinds  of  matter  have  very 
different  powers  of  stopping  Rontgen  rays,  it  is  possible  to 
photograph  the  bones  of  the  body,  although  the  flesh  is 
comparatively  transparent  to  them.  The  bones,  as  it 
were,  cast  their  shadow ;  or  the  shadow  of  the  bones  can 
be  thrown  on  a  piece  of  card,  painted  with  material  which 
phosphoresces  and  shines  when  exposed  to  the  impact  of 
the  rays. 

I  believe  that  Rontgen's  discovery  arose  from  an  acci- 
dental observation  that  a  box  of  photographic  plates  left 
near  a  Crookes's  tube  became  'fogged/  and  he  too  had 
genius  to  follow  up  this  clue. 


126    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

We  are  getting  on  rather  slowly,  however,  in  the  hunt 
for  an  explanation  of  flame.  A  great  step  in  advance  was 
made  by  the  discovery  of  radium  by  Madame  Curie. 

Radium  is  a  metal,  the  salts  of  which  continually  give 
out  '  Lenard  rays/  or  '  Crookes's  rays.'  And  it  is  certain 
that  it  is  losing  substance  during  their  emission. 

Mr.  Soddy  and  I  have  actually  trapped  and  measured 
one  of  the  products  which  is  being  thrown  off  by  radium 
while  these  rays  are  being  shot  out;  it  is  a  gas  called 
'  radium  emanation.'  And  it  in  its  turn  decomposes  and  is 
changed  to  some  extent  into  the  gaseous  element  helium, 
which  I  discovered  in  1895. 

All  the  while  that  these  changes  are  taking  place,  what 
are  called  '  /3-rays '  (beta-rays)  are  being  evolved,  and  the 
opinion  is  now  generally  held  that  these  so-called  rays  are 
really  negative  electricity,  and  are  identical  with  the 
'  cathode-rays '  of  Lenard. 

I  have  been  frequently  asked :  '  But  is  not  electricity  a 
vibration  ?  How  can  wireless  telegraphy  be  explained  by 
the  passage  of  little  particles  or  corpuscles  ? '  The  answer 
is  'Electricity  is  a  thing',  it  is  these  minute  corpuscles, 
but  when  they  leave  any  object,  a  wave,  like  a  wave  of 
light,  spreads  through  the  ether,  and  this  wave  is  used  for 
wireless  telegraphy.' 

It  has  been  found  that  flames  are  capable  of  conducting 
electricity,  while  gases,  under  the  usual  atmospheric 
pressure,  are  very  good  insulators,  and  sparks  can  pass 
through  air  only  when  the  current  is  one  of  very  high 
tension.  Now,  in  flames  rapid  chemical  action  is  taking 
place;  compounds  are  burning — that  is,  their  constituents 
are  in  the  act  of  uniting  with  oxygen. 

Although  it  is  not  certain  that  /3-rays— or,  to  give  their 
other  name,  corpuscles  of  electricity — are  being  shot  out 
during  such  changes,  it  is  not  improbable  that  they  are. 
No  doubt  they  impinge  on  the  neighbouring  atoms  and 


HOW  DISCOVERIES  ARE  MADE  127 

set  them  in  rapid  vibration ;  and  they  may  even  break  up 
molecules  and  cause  them  to  assume  other  forms  of 
combination.  And  in  doing  so,  very  short  electric  waves 
are  sent  out  through  the  ether,  and  these  are  what  we 
term  '  light/  and  '  radiant '  heat. 

There  are  several  other  lines  of  evidence  which  support 
this  notion.  For  example,  a  pure  gas  cannot  be  heated 
red-hot  or  made  to  glow  by  heat  alone.  There  must  be  a 
chemical  change  of  some  kind  at  the  same  time.  Again, 
a  Welsbach  incandescent  gas  mantle,  if  made  of  pure 
thoria  (and  that  means  '  nearly  pure,'  because  we  are  not 
acquainted  with  really  pure  substances),  does  not  give  out 
much  light  when  heated,  but  if  some  other  earth,  such  as 
oxide  of  cerium,  is  mixed  with  the  thoria,  the  familiar 
brilliant  incandescence  is  produced  when  it  is  heated  by  a 
Bunsen  burner.  The  '  pencil '  of  a  Nernst  lamp  is  made 
chiefly  of  zirconia,  another  earth ;  and  here,  again,  unless 
the  zirconia  is  mixed  with  a  trace  of  some  other  oxide,  it 
will  not  glow  very  brightly  when  a  current  of  electricity 
is  passed  through  it.  In  all  these  cases  there  is  almost 
certainly  chemical  change,  and  also,  no  doubt,  evolution  of 
corpuscles  of  electricity  which  set  the  ether  vibrating  and 
so  produce  light  and  heat. 

It  may  be  asked :  '  Do  substances  not  lose  weight  when 
corpuscles  are  being  shot  out  ? '  Professor  Landolt,  of 
Berlin,  has  been  making  experiments  on  the  gain  or  loss 
of  weight  when  a  weighed  quantity  of  substances  capable 
of  chemical  change  are  mixed  in  a  closed  vessel ;  and  he 
finds  that  in  many  cases  there  is  a  minute  loss  of  weight. 
Perhaps  that  is  due  to  the  escape  of  corpuscles ;  but  too  few 
experiments  have  been  made  to  allow  of  a  definite  answer.1 

Perhaps,  too,  the  corpuscles  when  expelled  are  not 
moving  very  rapidly,  and  are  thus  absorbed  by  the  sides 
of  the  vessel  in  which  the  reaction  takes  place ;  and  this 

1  He  has  since  shown  that  there  is  no  change  of  weight. 


128    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

may  also  be  the  case  with  flames.  A  flame,  however,  if 
brought  near  an  object  containing  an  electric  discharge 
will  discharge  it;  and  this  may  possibly  be  due  to  the 
action  of  electric  corpuscles  on  the  charged  object. 

It  will  be  seen,  then,  that  we  do  not  know  yet  with 
certainty  what  flame  is,  but  we  are  getting  on  the  track. 
And  the  direction  in  which  to  make  experiments  is  clear. 
Whosoever  asks  shall  receive,  but  he  must  ask  sensible 
questions  in  definite  order,  so  that  the  answer  to  the  first 
suggests  a  second,  and  the  reply  to  the  second  suggests  a 
third,  and  so  on.  If  that  course  be  followed,  it  will 
certainly  result  in  discoveries,  many  of  which  may  be 
important  and  lead  to  inventions  of  great  practical  value. 
For,  indeed,  an  invention  is  often  definable  as  a  method 
for  utilising  a  discovery. 


THE  BECQUEREL  RAYS1 

IT  is  remarkable  how  the  writings  of  ancient  authors  often 
contain  a  forecast  of  subsequent  discoveries.  Puck's  pro- 
jected girdle  round  the  earth,  which  was  promised  com- 
pletion in  forty  minutes,  has  been  surpassed  many  hundred 
times  by  the  rate  of  the  electric  current  in  a  telegraph- 
wire  ;  and  Robert  Boyle's  suggestions  regarding  the  nature 
of  the  air  are  on  the  high-road  towards  verification.  He 
wrote,  about  the  year  1670:  'Our  atmosphere,  in  my 
opinion,  consists  not  wholly  of  purer  aether,  or  subtile 
matter  which  is  diffused  thro'  the  universe,  but  in 
great  number  of  numberless  exhalations  of  the  terr- 
aqueous globe;  and  the  various  materials  which  go  to 
compose  it,  with  perhaps  some  substantial  emanations  from 
the  celestial  bodies,  make  up  together,  not  a  bare  indeter- 
mined  feculancy,  but  a  confused  aggregate  of  different 
effluvia.' 

Up  to  1894,  it  was  supposed  that  our  atmosphere  con- 
sisted mainly  of  the  two  gases,  nitrogen  and  oxygen,  together 
with  minute  quantities  of  carbonic  acid,  water- vapour, 
ammonia,  peroxide  of  hydrogen,  and  ozone ;  but  in  that 
year  it  was  shown  to  contain  a  not  inconsiderable  amount 
of  an  inactive  gas,  argon ;  and  crude  argon  has  since  been 
found  to  contain  minute  quantities  of  no  fewer  than  four 
other  similar  gases.  Small  traces  of  hydrogen  have  also 
been  discovered  in  air;  although  a  large  percentage  of 

1  An  article  which  appeared  in  the  Contemporary  Review,  1902. 

I 


130    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

hydrogen  would  render  air  explosive  (for  water  is  formed 
with  explosive  violence  when  hydrogen  and  oxygen  com- 
bine), yet  traces  of  hydrogen  may  coexist  with  oxygen 
without  combination,  except  when  the  mixture  is  actually 
in  contact  with  a  flame. 

These,  however,  are  not  the  only  constituents  of  the 
atmosphere ;  and  in  the  following  pages  an  account  will 
be  given  of  certain  phenomena  which  render  it  exceed- 
ingly probable  that  still  more  '  subtile  matter '  is  on  the 
eve  of  discovery. 

In  order  to  follow  the  course  of  events,  it  is  first  neces- 
sary to  devote  some  attention  to  the  supposed  nature  of 
light.  Owing  to  its  being  perceived  by  our  special  organ 
of  sense,  the  eye,  it  early  attracted  attention.  At  first 
believed  to  consist  of  corpuscles,  shot  out  from  the  lumin- 
ous body,  it  is  now  recognised  as  arising  from  the  vibra- 
tions of  a  medium  pervading  all  space,  termed  ether ;  and 
the  propagation  of  light  takes  place  much  as  waves  spread 
in  a  pond,  except  in  this :  the  particles  of  ether,  unlike 
the  waves  of  water,  are  not  restricted  in  their  motion  to 
one  plane,  but  the  oscillations  may  take  place  in  all  direc- 
tions at  right  angles  to  the  direction  of  propagation. 
There  appears,  however,  to  be  no  limit  to  the  mode  or 
magnitude  of  the  ethereal  waves ;  and  though  it  cannot  be 
positively  stated  that  the  wave-motion  ever  takes  place, 
like  sound  waves,  in  the  direction  of  propagation,  still  that 
mode  of  propagation  of  waves  is  not  excluded.  It  is  cer- 
tain, however,  that  such  a  mode  of  transmission  does  not 
correspond  with  the  nature  of  light,  which  consists  wholly 
of  transverse  vibrations. 

Just  as  it  is  possible  to  measure  the  distance  between 
the  crests  of  the  waves  of  the  sea,  so  it  is  possible  to  deter- 
mine the  distance  between  the  crests  of  the  waves  of  light, 
or  in  other  words,  to  measure  the  wave-length  of  light. 
And  it  has  been  discovered  that  all  the  visible  rays  of 


THE  BECQUEREL  RAYS  131 

light  are  comprised  in  less  than  an  octave;  that  is,  the 
longest  visible  waves  are  not  twice  as  long  as  the  shortest 
visible.  Their  length,  moreover,  is  not  inconceivably 
minute.  The  twenty-fifth  part  of  an  inch,  or  a  millimetre, 
although  a  small  distance,  is  easily  seen  with  the  naked 
eye ;  indeed,  the  twentieth  part  of  that  length  can  still  be 
estimated  without  the  aid  of  a  lens.  The  average  length 
of  a  light- wave  is  about  the  hundredth  part  of  that  dis- 
tance, or  about  the  two-thousandth  of  a  millimetre.  The 
thousandth  part  of  a  millimetre  is  termed  a  micron,  the 
symbol  for  which  is  the  Greek  letter  //, ;  the  wave-length 
of  deep  red  light  is  f/z,  and  of  violet  light  f//,. 

There  are,  however,  ethereal  waves  which  cannot  be 
seen.  Those  of  greater  wave-length  give  rise  to  the  sensa- 
tion of  heat ;  they  are  termed  '  infra-red '  waves ;  while 
those  of  shorter  period  are  accessible  to  photography,  for 
they  change  the  nature  of  the  compounds  of  silver  which 
form  the  sensitive  coating  of  a  photographic  plate,  and 
can  thus  be  recognised ;  they  are  termed  '  ultra-violet ' 
waves.  One  of  the  difficulties  of  tracing  the  existence  of 
the  short  wave-lengths  by  photography  consists  in  the 
absorptive  power  which  glass  and  air  have  for  such  waves. 
A  pane  of  glass,  though  transparent  to  ordinary  light 
waves,  is  nearly  opaque  to  ultra-violet  waves.  Quartz  or 
crystal,  of  which  spectacle-lenses  are  generally  made,  is 
much  more  transparent  to  vibrations  of  short  wave- 
lengths ;  but  even  quartz  has  its  limits.  By  an  ingenious 
contrivance  for  exposing  a  sensitive  plate  in  a  vacuum,  so 
that  the  absorption  of  the  air  did  not  influence  the  result, 
Schumann  succeeded  in  chronicling  the  existence  of  waves 
only  -^Q/JU  in  length.  On  the  other  hand,  Langley,  by 
means  of  an  exceedingly  delicate  apparatus  for  detecting 
heat-vibrations,  termed  a  bolometer,  has  detected  waves 
as  long  as  30 p.  Between  that  wave-length  and  one  two 
hundred  times  as  great,  six  millimetres,  there  is  a  gap  in 


132    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

our  knowledge ;  the  longer  waves  are  the  vibrations  the 
discovery  of  which  was  due  to  Hertz,  which  are  produced 
by  electric  oscillations,  and  which  are  now  being  utilised 
for  telegraphy  without  wires. 

It  is,  however,  with  the  shorter,  and  not  with  the  longer 
vibrations,  that  we  have  to  do.  These  are  not  incom- 
mensurable with  the  dimensions  of  a  molecule,  for  the 
larger  molecules  are  believed  to  be  about  the  millionth 
of  a  millimetre  in  diameter,  or  about  one  hundredth  of 
the  shortest  wave-length  which  has  been  measured.  And 
just  as  an  interposed  grating  offers  little  opposition  to  the 
course  of  a  large  wave  of  water,  while  it  will  stop  ripples, 
so  matter  is  sufficiently  fine-grained  not  to  oppose  the 
spread  of  a  Hertzian  wave  of  great  wave-length,  although 
it  may  stop  light  and  other  vibrations  of  shorter  wave- 
length. It  is  known,  indeed,  that  the  signals  of  wireless 
telegraphy  are  not  blocked  by  material  obstacles  such  as 
houses,  or  even  hills,  while  a  very  thin  slice  of  brick  or 
stone  is  opaque  to  light. 

When  two  thin  strips  of  gold-leaf  are  suspended  from  a 
glass  support,  and  given  an  electric  charge,  they  diverge, 
owing  to  the  repulsive  force  between  the  charges  of  elec- 
tricity which  they  contain.  They  will  remain  apart  for 
an  indefinite  time,  provided  the  charge  cannot  escape 
through  the  support.  But  on  exposure  to  ultra-violet 
rays,  the  electroscope,  if  charged  with  negative  electricity, 
is  at  once  discharged,  and  the  leaves  fall  together.  The 
electricity  finds  some  means  of  leaving  the  leaves  of  gold 
and  they  drop,  under  the  action  of  gravity.  The  rays  do 
not,  however,  discharge  a  positively  charged  electroscope. 
This  is  one  of  the  most  characteristic  properties  of  the 
ultra-violet  rays,  and,  as  will  shortly  be  seen,  of  rays  from 
sources  other  than  luminous  bodies.  This  fact  was  dis- 
covered by  Hertz. 

The  Becquerel  family  has  contributed  much  to  our 


THE  BECQUEREL  RAYS  133 

knowledge  of  the  phenomena  of  radiation,  and  furnishes 
as  conspicuous  an  example  as  the  Herschels  of  the  her- 
edity of  a  scientific  faculty.  Antoine  Charles,  born  in 
1788,  was  famous  for  his  electric  researches;  Edmond,  his 
son,  born  in  1820,  was  author,  with  his  father,  of  a  treatise 
on  Electricity  and  Magnetism,  and  investigated  the  phe- 
nomenon of  phosphorescence,  of  which  more  anon ;  and 
Henri  Becquerel,  born  in  1852,  while  engaged  in  extend- 
ing his  father's  work,  made  the  wonderful  discovery  of 
the  emission  of  rays  from  certain  minerals  containing 
the  rare  metals  uranium  and  thorium.  We  must  first, 
however,  consider  Edmond  Becquerel's  work. 

Certain  substances,  after  illumination,  do  not  at  once 
cease  to  give  back  light,  but  continue  to  glow,  even  after 
the  source  of  light  has  been  removed.  Such  substances, 
one  of  the  best  known  of  which  is  fluor-spar,  are  called 
phosphorescent.  Some  years  ago,  an  attempt  was  made  to 
utilise  one  of  such  substances — a  carbonate  of  lime  con- 
taining traces  of  sulphide  of  manganese — under  the  name 
of '  luminous  paint.'  Another  class  of  substances  has  the 
property  of  transforming  the  vibrations  they  receive  when 
illuminated  into  vibrations  of  a  different  period;  among 
these  are  extract  of  horse-chestnut,  and  many  artificial 
colouring-matters,  one  of  the  most  striking  being  the 
lovely  pink  dye,  eosin.  Such  bodies  do  not  continue  to 
emit  light  after  excitation ;  they  were  differentiated  from 
the  former  by  Edmond  Becquerel,  and  are  termed  fluor- 
escent. The  tendency  of  these  substances  is  to  convert 
short  wave-lengths  into  longer  ones.  Thus  a  solution  of 
acid  sulphate  of  quinine,  which  is  perfectly  colourless  by 
transmitted  light,  is  opaque  to  ultra-violet  rays.  It  reflects 
them,  and  at  the  same  time  increases  the  wave-length ; 
hence  by  reflected  light  the  solution  appears  to  possess  a 
violet  shimmer. 

It  was  in  1838  that  Faraday  investigated  the  luminous 


134    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

appearance  which  accompanies  the  passage  of  a  high- 
tension  electric  current  through  rarefied  gases.  Each  gas 
gives  out  a  soft,  coloured  light,  totally  different  from  the 
lightning-like  sparks  which  pass  between  the  positive  and 
negative  poles  through  gases  at  ordinary  atmospheric 
pressure.  The  pressure  must  be  reduced  to  about  one- 
hundredth  of  its  normal  amount  before  such  phenomena 
begin  to  appear;  but  the  actual  reduction  of  pressure 
depends  on  the  particular  gas  submitted  to  the  dis- 
charge. Under  such  conditions  hydrogen  glows  with  a 
red  light ;  air  with  a  pale  violet  glow ;  and  carbonic  acid 
has  a  steel  blue  appearance.  The  resistance  of  such 
rarefied  gases  to  the  passage  of  the  electric  current  is 
much  less  than  of  gases  at  atmospheric  pressure.  As  with 
solid  conductors,  it  depends  on  the  distance  between  the 
poles  and  the  particular  kind  of  matter  employed. 
Hittorf,  the  eminent  electrician,  Professor  in  Miinster, 
was  the  first  to  conduct  experiments  at  still  lower 
pressures,  on  still  more  rarefied  gases,  and  he  noted  an 
increase  in  the  resistance  of  the  gas  to  the  passage  of 
electricity.  Further,  he  observed  that  from  the  negative 
electrode,  or  cathode,  the  glow  proceeded  in  straight  lines, 
so  as  to  cast  the  shadow  of  an  interposed  object  on  the 
opposite  wall  of  the  tube.  He  discovered,  too,  that  such 
rays  can  be  deviated  by  a  magnet,  a  discovery  made  for 
the  electric  arc  by  Sir  Humphry  Davy  in  1821.  Sir 
William,  then  Mr.,  Crookes  took  up  this  subject  in  1878, 
simultaneously  with  M.  Goldstein,  and  has  made  it 
popular,  by  reason  of  the  ingenious  experiments  which  he 
devised  to  exhibit  the  rectilinear  course  of  these  rays. 
He  devised  a  theory,  moreover,  to  account  for  the  recti- 
linear path,  namely,  that  the  electric  current  when  it 
leaves  the  negative  pole  attaches  itself  to  the  molecules  of 
gas,  which,  projected  with  great  velocity,  will  pursue  a 
parallel  path,  if  the  cathode  is  a  flat  piece  of  metal,  or  can 


THE  BECQUEREL  RAYS  135 

be  focussed  to  a  point,  if  the  cathode  be  given  the  form  of 
a  concave  mirror.  Objects  placed  in  the  focus  of  such  a 
mirror  are  bombarded,  according  to  Sir  William,  and  may 
be  heated  to  whiteness  by  the  impacts  they  receive  from 
the  prodigious  number  of  moving  molecules.  Goldstein, 
on  the  other  hand,  conceived  the  phenomena  to  be  due  to 
a  transmission  of  energy,  apart  from  the  conveyance  of 
material  particles ;  but  he  gave  no  precise  definition  of  the 
nature  of  this  transmitted  energy.  In  1883,  however, 
Professor  Wiedemann  of  Leipzig  made  the  suggestion 
that  possibly  such  '  cathode  rays/  as  the  rectilinear  dis- 
charges have  since  been  termed,  are  composed  of  radia- 
tions of  very  short  wave-length,  shorter  even  than  those 
of  the  most  ultra-violet  light.  The  same  conception  was 
held  by  Lenard.  But  while  the  cathode  rays  are  deviated 
by  a  magnet,  light  waves  are  uninfluenced ;  and  this  forms 
an  argument  in  favour  of  the  former  being  due  to  pro- 
jected particles.  The  suggestion  has  also  been  made,  but 
on  no  sufficient  grounds,  that  these  phenomena  are  attri- 
butable to  a  longitudinal  vibration  of  the  ether,  the  waves 
being  thus  analogous  to  sound-waves  in  air — alternate 
condensations  and  rarefactions;  or  to  choose  a  visible 
analogy,  the  longitudinal  vibrations  of  a  spiral  spring,  in 
which  the  coils  periodically  come  closer  together  at  one 
point  of  space,  and  then  recede  and  become  wider  apart. 
A  fourth  hypothesis,  similar  to,  yet  differing  from  that  of 
Crookes,  is  held  by  Professor  J.  J.  Thomson  of  the 
Cavendish  Laboratory,  Cambridge.  His  view,  which 
appears  to  be  well  supported  by  experimental  evidence, 
is  that  each  molecule  of  gas,  in  absorbing  its  electric 
charge,  dissociates,  or  splits  up,  into  two  or  more  charged 
atoms  or  groups  of  atoms.  Such  charged  portions  of 
matter  have  long  been  taken  for  granted  as  existing 
during  the  passage  of  an  electric  current  through  a  con- 
ducting liquid,  and  were  named  by  Faraday,  ions,  or 


136    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

travellers.  An  important  argument  in  favour  of  this 
contention  is,  that  the  heat  developed  in  such  tubes  is 
proportional  to  the  intensity  of  the  current,  and  not  to  the 
square  of  the  intensity,  as  would  be  the  case  were  the 
passage  of  electricity  one  of  ordinary  conduction.  Thomson 
attributes  the  heat  to  the  recombination  of  the  ions  to 
molecules,  after  discharge ;  and  the  number  of  ions  would 
obviously  be  proportional  to  the  intensity  of  the  current 
and  not  to  its  square. 

Goldstein  and  Crookes  both  thought  that  ordinary 
matter,  such  as  glass  or  metal,  was  opaque  to  such 
cathode-discharges ;  but  Lenard,  following  a  suggestion  of 
Hertz's,  carried  out  at  Bonn  a  beautiful  series  of  experi- 
ments, which  showed  that  the  cathode  rays  could  pass 
through  a  thin  piece  of  aluminium  foil,  and  be  prolonged 
outside  of  the  exhausted  tube.  Not  only  could  they  pass 
through  ordinary  air,  although  not  to  such  a  distance  as 
through  rarefied  gases,  but  they  also  passed  through  a 
vacuum  as  perfect  as  could  be  produced  by  a  mercury- 
pump,  aided  by  intense  cold  to  condense  mercury- vapour 
out  of  the  empty  space.  It  appeared  that  the  absorbing 
power  of  different  gases  is  proportional  to  their  specific 
mass. 

The  velocity  of  propagation  of  such  cathode  rays  has 
been  measured  by  an  ingenious  process  by  Professor  J.  J. 
Thomson.  It  is  found  to  be  approximately  200  kilo- 
metres, or  about  124  miles  a  second.  This,  however,  is 
enormously  less  than  the  velocity  of  light  or  of  electric 
waves  through  the  ether,  which  approximates  to  180,000 
miles  a  second.  The  accidental  discovery  by  Professor 
Eontgen  in  1896  that  some  flakes  of  platinocyanide  of 
barium,  placed  near  a  Hittorf  tube  which  was  wrapped  up 
in  black  paper,  emitted  a  phosphorescent  light,  led  to  a 
great  development  of  the  subject.  It  was  soon  discovered 
that  even  behind  a  book  of  1000  pages,  or  a  plate  of 


THE  BECQUEREL  RAYS  137 

aluminium  half  an  inch  thick,  or  a  wooden  board,  lumin- 
escence was  still  produced.  Rontgen  investigated  the 
transparency  of  various  objects,  and  soon  discovered  that 
while  skin  and  flesh  are  nearly  transparent  to  these 
radiations,  bone  is  comparatively  opaque,  and  may  be 
made  to  throw  its  shadow  on  a  photographic  plate  or  on  a 
screen  covered  by  phosphorescent  material.  The  surgical 
bearing  of  this  discovery  was  at  once  evident ;  and  by  help 
of '  skiographs '  or  shadow-writing  the  presence  of  a  bullet 
embedded  in  the  tissue  can  be  recognised,  and  its  exact 
situation  localised ;  and  in  cases  of  fractures  of  bones, 
their  exact  shape  can  be  made  out,  and  they  can  be 
successfully  set,  for  it  is  always  possible  to  examine  the 
position  of  the  fractured  ends  through  envelopes  of 
bandages,  which  themselves  are  nearly  transparent  to 
Rontgen  or  X-rays. 

One  of  the  most  remarkable  properties  of  these  rays  is 
that  they  cannot  be  refracted  by  passage  through  a  prism, 
nor  apparently  reflected  from  any  object,  however  smooth 
and  well-polished,  nor  can  they  be  polarised.  They  are, 
however,  absorbed  by  different  substances  unequally,  and 
apparently  the  denser  the  substance  the  greater  its  absorb- 
ing power. 

It  might  be  supposed  at  first  blush  that  the  X-rays  of 
Rontgen  were  identical  with  cathode  rays.  But  if  this 
were  the  case  the  X-rays  should  pass  straight  from  the 
cathode  through  the  walls  of  the  tube,  and  proceed  in  a 
straight  line  ;  as  a  matter  of  fact,  their  point  of  origin  can 
be  displaced  with  a  magnet,  and  if  a  spherical  bulb  be 
used  to  contain  the  cathode,  each  point  on  the  bulb  is  a 
centre  of  emission,  sending  its  radiations  in  all  directions. 
Now  Lenard  had  recognised  that  cathode  rays  could  be 
differentiated  into  two  distinct  kinds.  Suppose  that  they 
were  made  to  pass  through  a  hole  in  a  block  of  lead,  and  to 
impinge  on  a  photographic  plate,  if  a  magnet  were  placed 


138    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

at  one  side,  not  only  was  there  the  image  of  a  circle 
exactly  opposite  the  hole,  but  also,  at  some  distance  from 
the  circular  spot,  a  diffused  drawn-out  impression,  as  if 
some  of  the  rays  had  been  unequally  deviated  by  the 
magnet,  and  had  impressed  the  plate  separately.  It  is 
therefore  probable  that  cathode  rays  contain  some 
X-rays. 

The  wave-length  of  light  can  be  measured  by  reflection 
from  a  metal  plate  on  which  from  14,000  to  25,000  parallel 
lines  are  ruled  in  each  inch;  such  a  prepared  plate  is 
termed  a  '  grating ' ;  the  modern  gratings,  which  are 
wonderfully  accurately  ruled,  are  made  by  Mr.  Brashier 
of  Alleghany,  New  York  State,  by  means  of  apparatus 
devised  by  the  late  Professor  Rowland  of  Baltimore. 
Careful  measurements  by  M.  Perrin  have  proved  that  if  the 
X-rays  are  due  to  ethereal  vibrations  at  all,  these  cannot 
possess  a  wave-length  greater  than  0*04  /JL,  that  is,  less  than 
half  the  shortest- waved  ultra-violet  vibrations  which  have 
ever  been  photographed. 

Again,  when  light  is  passed  through  a  slice  cut  from 
a  crystal  of  tourmaline  it  is  said  to  be  polarised ;  it  can 
pass  through  a  second  plate  of  tourmaline  if  held  in  a 
particular  position,  but  if  the  second  plate  be  rotated  so 
that  its  second  position  is  at  right  angles  to  its  first,  the 
light  is  cut  off,  and  fails  to  pass  through  the  second  plate. 
M.  Becquerel  found  that  X-rays  cannot  be  polarised ;  they 
pass  easily  through  plates  of  tourmaline  in  whatever 
position  relatively  to  each  other  they  be  placed.  On  the 
other  hand,  the  rays  emitted  by  phosphorescent  bodies, 
which  may  be  termed  the  Becquerel  rays,  are  capable  of 
polarisation.  Hence  they  cannot  be  identical  with  X-  or 
with  cathode  rays. 

Lastly,  it  will  be  remembered  that  ultra-violet  rays 
discharge  negatively  electrified  bodies;  they  are  without 
rapid  action  on  bodies  possessing  a  positive  charge.  But 


THE  BECQUEREL  RAYS  139 

X-rays  discharge  electrified  bodies  equally  well,  whether 
they  be  charged  positively  or  negatively.  - 

There  is  accordingly  a  certain  degree  of  probability  in 
favour  of  the  view  that  cathode  rays  are  due  to  molecular 
or  ionic  bombardment ;  but  they  are  generally  mixed  with 
X-rays,  which  are  apparently  independent  of  matter  for 
their  propagation,  and  are  therefore  to  be  considered  as 
due  to  disturbances  of  the  ether.  Ultra-violet  rays,  on 
the  other  hand,  must  be  ethereal  waves  of  very  short 
wave-length ;  but  they  have  the  power  of  splitting  gaseous 
molecules  into  charged  atoms  or  groups  of  atoms,  termed 
ions.  It  may  be  calculated,  too,  that  the  atoms  conveying 
cathode-rays  have  a  velocity  of  124  miles  a  second;  it 
would  follow  that  of  such  atoms  a  single  gram,  or  about 
one- thirtieth  of  an  ounce,  must  have  the  same  energy  as 
a  locomotive  of  80  tons  weight  rushing  at  the  rate  of 
50  miles  an  hour !  No  wonder,  .then,  that  they  penetrate 
thin  sheets  of  metal  and  embed  themselves  in  glass. 

In  1896  M.  Poincare,  the  well-known  mathematician, 
suggested  that  all  fluorescent  substances  might  emit 
Rontgen  rays;  being  guided  to  this  guess  by  the  hypo- 
thesis that  it  is  the  glass,  against  which  the  Rontgen  rays 
strike,  which  phosphoresces  and  emits  the  rays.  This 
suggestion  was  almost  at  once  verified  by  M.  Charles 
Henry,  when  he  discovered  that  sulphide  of  zinc,  a  sub- 
stance which  shows  marked  phosphorescence,  greatly 
increases  the  effect  of  X-rays  when  placed  in  their  path. 
M.  Henri  Becquerel,  too,  in  the  same  year,  found  that  rays 
were  emitted  from  a  compound  of  the  metal  uranium, 
which  affected  a  photographic  plate  wrapped  in  black 
paper,  sufficient  to  exclude  rays  of  direct  sunlight.  This 
power  to  affect  a  sensitised  plate  persists  long  after  all 
visible  phosphorescence  ceases.  Moreover,  it  is  unneces- 
sary to  expose  uranium  salts  to  light  before  they  are 
capable  of  producing  a  photographic  image,  for  these 


140    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

compounds  may  be  prepared  in  the  dark  and  still  possess 
actinic  power.  And  the  rays  emitted  from  them  have  the 
power  of  discharging  both  positively  and  negatively 
electrified  bodies.  Not  merely  salts  of  uranium  possess 
this  property,  but  even  metallic  uranium  itself,  a  dark- 
coloured,  brittle  metal,  which  emits  sparks  of  fire  when 
shaken  in  a  bottle,  a  phenomenon  due  probably  to 
oxidation. 

Shortly  after  this  discovery  of  Becquerel's,  Madame 
Curie,  a  Polish  lady  working  in  Paris,  discovered  that  a 
certain  specimen  of  pitchblende,  the  common  ore  of 
uranium,  possesses  the  properties  of  uranium,  and  in 
greater  measure.  Pitchblende,  though  consisting  mainly 
of  an  oxide  of  uranium  of  the  formula  U308,  contains 
small  amounts  of  other  elements.  On  separating  these, 
Monsieur  and  Madame  Curie  found  that  the  bismuth 
obtained  from  this  source  is  particularly  radio-active, 
while  ordinary  bismuth  shows  no  trace  of  that  property. 
Attributing  this  behaviour  to  its  containing  a  new  element, 
they  patriotically  named  it  '  polonium/  in  allusion  to 
Madame  Curie's  nationality.  But  it  was  not  long  before 
they  discovered  that  it  was  not  only  the  bismuth  which 
exhibited  radio-activity,  but  also  the  barium ;  and  they 
inferred  the  presence  of  a  second  element,  naming  it 
'radium.'  A  third  substance  has  also  been  separated 
from  the  same  uranium  ores  by  Debierne,  who,  following 
precedent,  has  termed  it  'actinium.'  It  appears  to  be 
associated  with  another  element,  titanium,  contained  in 
pitchblende ;  and  thorium,  an  element  whose  compounds 
were  discovered  to  possess  radio-activity  by  G.  C.  Schmidt, 
must  be  added  to  the  list.  We  have  therefore  at  present 
no  fewer  than  four  radio-active  substances :  polonium, 
associated  with  bismuth ;  radium,  with  barium ;  actinium, 
with  titanium  ;  and  thorium.  Associated  with  thorium  is 
a  much  more  powerfully  radio-active  material,  to  which 


THE  BECQUEREL  RAYS  141 

the  name  radio-thorium  was  applied  by  its  discoverer, 
Otto  Hahn. 

Besides  the  properties  already  mentioned,  radium,  and 
presumably  the  others,  have  the  curious  property  of 
changing  a  spark-discharge  from  an  electric  machine  or 
a  Ruhmkorffs  coil  into  a  violet  glow-discharge;  the 
interposition  of  a  piece  of  lead,  however,  re-establishes 
the  spark-discharge ;  and  if  barium  bromide  containing 
radium  be  held  on  the  forehead  between  the  closed  eyes 
in  a  dark  room,  a  distinct  luminous  haze  is  visible  after 
a  few  seconds.  The  actinium  rays,  indeed,  are  said  to  be 
100,000  times  as  powerful  as  those  of  uranium.  Very 
powerfully  radio-active  preparations  of  barium  chloride 
and  bromide  are  now  manufactured  by  various  firms  by 
processes  devised  by  Madame  Curie  and  by  Professor 
Giesel. 

A  new  light  has  been  thrown  on  all  these  phenomena 
by  Professor  Rutherford,  who  has  found  that  thorium 
compounds  give  out  an  '  emanation,'  which  may  be  likened 
to  one  of  Boyle's  '  exhalations  of  the  terraqueous  globe.' 
Dr.  Russell  had  previously  discovered  that  photographic 
plates  are  affected  by  hydrogen  dioxide  vapour,  which 
appears  to  be  produced  in  small  amount  under  the  most 
varying  conditions ;  but  Rutherford's  exhalations  persisted 
under  treatment  which  would  have  been  fatal  to  hydrogen 
dioxide ;  moreover,  these  emanations  rapidly  discharge 
electrified  bodies,  a  property  which  hydrogen  dioxide  does 
not  possess.  The  existence  of  such  emanations  (of  which 
more  hereafter)  must  be  borne  in  mind  in  forming  a 
judgment  of  the  statements  made  about  these  various 
radiations. 

Radio-active  substances  can  communicate  transitory 
radio-activity  to  all  kinds  of  matter,  metals,  glass,  paper, 
etc.,  which  then  for  a  short  time  possess  radio-activity 
equal  to  ninety  times  that  of  uranium.  They  lose  the 


142    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

property  more  rapidly,  however,  when  heated  or  washed. 
Even  distilled  water  acquires  radio-activity,  when  placed 
near  radium  chloride  under  a  glass  bell-jar;  the  water 
rapidly  loses  its  power  in  an  open  vessel  after  removing 
it  from  the  proximity  of  the  radium;  and  even  when 
sealed  into  a  glass  tube  it  loses  power  after  a  few  days. 
On  the  other  hand,  a  solution  of  a  radium  salt  (e.g.  radio- 
active barium  bromide)  loses  activity  on  exposure  to  air, 
but  regains  it  on  being  kept  in  a  sealed  tube. 

MM.  Curie  and  Debierne  find  that  this  induced  radio- 
activity is  greatly  increased  when  the  radium  compound 
is  placed  in  a  small  open  vessel  under  a  bell-jar,  and  sheets 
of  various  materials  are  exposed  under  the  same  cover. 
Even  behind  leaden  screens  the  activity  is  induced.  If 
they  are  in  contact  with  the  vessel  containing  the  radium, 
or  with  the  walls  of  the  enclosed  space,  only  the  exposed 
surfaces  are  rendered  radio-active.  The  activity  of  such 
sheets  of  material  induced  by  a  specimen  of  barium 
bromide  containing  radium,  and  of  which  the  mean  atomic 
weight  of  the  mixture  of  metals  is  174  instead  of  137  (that 
of  barium),  is  8000  times  that  of  a  piece  of  uranium  of  the 
same  dimensions.  As  long  as  the  sheets  are  left  in  the 
enclosure,  the  activity  persists;  if  removed,  it  disappears 
in  a  few  days.  This  conveyance  of  induced  radio-activity 
is  equally  brought  about  if  the  radium  compound  is 
placed  in  one  vessel,  and  the  sheets  in  another,  connected 
with  the  former  by  means  of  a  capillary  tube ;  but  if 
communication  between  the  vessels  is  cut  off,  the  trans- 
mission of  activity  ceases. 

It  is  very  remarkable  that  this  transference  of  radio- 
activity is  confined  to  radium  and  actinium;  polonium 
compounds  do  not  appear  to  possess  the  property  of 
giving  off  emanations.  It  may  be  that  this  difference 
is  connected  with  the  fact  discovered  by  Becquerel  that 
while  his  rays  (those  of  radium  and  actinium,  probably), 


THE  BECQUEEEL  RAYS  143 

like  cathode  rays,  are  deviable  by  a  magnet,  those  of 
polonium  resemble  X-rays  in  being  unaffected.  Curie, 
on  the  other  hand,  states  that  both  deviable  and  undevi- 
able  rays  are  emitted  from  radium  as  well  as  from 
polonium,  and  that  the  non- deviable  rays  are  stopped  by 
a  piece  of  thin  aluminium  foil.  None  of  these  rays  appear 
to  be  polarisable,  nor  do  they  show  refraction  when  passed 
through  a  prism. 

Becquerel  also  discovered  that  air,  left  in  contact  with 
some  radio-active  substances,  discharges  electrified  bodies  ; 
indeed,  it  is  impossible  to  charge  an  insulated  conductor 
in  a  room  in  which  any  such  preparations  have  been 
exposed.  This  power  of  inducing  air  to  discharge  electri- 
fied bodies  persists  for  at  least  a  year,  even  although  the 
preparation  has  been  kept  in  the  dark  all  the  time;  it 
cannot  therefore  be  supposed  that  light-energy  is  in  any 
way  transformed  into  such  radiations. 

In  Curie's  experiments  on  induction  it  was  found  that 
provided  the  vessel  containing  radium  was  kept  vacuous, 
the  emanations  had  no  longer  the  property  of  inducing 
radio-activity  in  sheets  of  metal,  etc.,  exposed  in  the  same 
vessel.  It  appears  possible,  therefore,  to  pump  off  the 
radio-active  matter ;  and  the  natural  conclusion  is  that 
it  is  a  gas.  The  gaseous  matter  has  been  collected,  or  at 
least  air  charged  with  it,  and  it  displays  marked  chemical 
action,  as  well  as  high  radio-activity.  It  converts  oxygen 
into  ozone,  and  the  glass  vessels  which  contain  it,  if 
formed  of  soda-glass,  turn  violet,  and  then  black,  owing 
to  some  change.  Becquerel,  too,  remarks  on  the  destruc- 
tive action  of  radium  rays  on  the  skin;  they  discolour 
rock-salt,  change  yellow  phosphorus  to  red,  and  destroy 
the  germinating  power  of  mustard  and  cress  seeds. 

On  the  hypothesis  that  the  radiation  of  radium  is 
produced  by  the  escape  of  material  particles  which 
bombard  the  walls  of  the  containing  vessel,  the  velocity 


144    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

of  such  particles  can  be  determined  by  a  device  which 
may  be  illustrated  thus :  Imagine  a  bullet  fired  from  a 
rifle  placed  horizontally,  at  some  little  distance  above  the 
ground ;  the  bullet  will  be  attracted  to  the  earth,  and  will 
fall  to  the  ground  after  it  has  gone  a  certain  distance. 
The  factors  which  determine  the  spot  at  which  it  will 
strike  the  ground  (excluding  the  retarding  influence  of 
air)  are  its  speed,  and  the  attraction  of  the  earth.  If  the 
attraction  is  known,  the  speed  can  be  calculated.  This 
analogy  illustrates,  although  imperfectly,  the  method  of 
arriving  at  the  speed  of  these  impelled  particles.  They 
are  deviated  by  a  magnetic  field,  and  have  a  trajectory 
just  as  a  rifle-bullet  has;  and  their  speed  has  been  cal- 
culated by  Becquerel  at  160,000  kilometres  or  100,000 
miles  per  second.  This  estimate  differs  greatly  from  the 
one  previously  mentioned  for  cathode  rays. 

In  conclusion,  it  has  been  suggested  that  the  existence 
of  such  radiations  and  emanations  may  be  attributed  to 
the  existence  of  '  electrons  '  in  the  free  state.  An  electron, 
it  may  be  explained,  is  an  electric  charge  which  attaches 
itself  to  an  atom  of  an  element,  thereby  converting  it  into 
an  ion.  The  act  of  solution  in  water  of  such  a  substance 
as  common  salt  is  now  currently  held  to  cause  the  atom 
of  sodium  to  separate  from  the  chlorine  atom,  while  each 
acquires  an  electric  charge,  the  sodium  combining  with  a 
positive  electron,  the  chlorine  with  a  negative  one,  thus : 
NaCl  +  water  +  ®©  =  Na®  +  water  +  Cl©  + 
water;  the  neutral  molecule  of  electricity,  consisting  of 
two  oppositely  charged  electrons  being  thus  dissociated. 
Now  it  is  conceivable  that  such  a  substance  as  pitchblende 
or  its  radio-active  constituents  may  combine  with  one  of 
the  electrons,  liberating  the  other.  It  has,  indeed,  been 
shown  by  the  Curies  that  radium  rays  charge  negatively 
the  bodies  which  receive  them,  while  the  radium  prepara- 
tion acquires  a  positive  charge. 


THE  BECQUEREL  RAYS  145 

Whatever  be  the  true  explanation  of  these  mysteries, 
it  cannot  be  denied  that  they  form  the  beginnings  of 
what  may,  and  almost  certainly  will,  affect  the  material 
future  of  the  human  race.  When  we  consider  the  begin- 
nings made  by  Gilbert,  by  Franklin,  by  Volta,  and  by 
Faraday,  and  contrast  them  with  the  outcome  of  these 
discoveries,  the  electric  telegraph,  and  the  dynamo 
machine,  we  cannot  avoid  the  inference  that  the  future 
has  in  store  even  greater  developments  than  these.  It 
is  true  that  investigators  like  Hertz,  Lenard,  Becquerel, 
and  the  Curies  do  not  make  practical  application  of  their 
discoveries;  but  there  is  never  any  lack  of  men  who 
discover  their  practical  value,  and  apply  them  to  ends 
useful  to  mankind.  All  the  more  reason,  therefore,  that 
every  encouragement  should  be  given  to  the  investigator, 
for  it  is  to  him  that  all  our  advances  in  physical  and 
material  well-being  are  ultimately  due. 


K 


WHAT  IS  AN  ELEMENT? 

IT  was  for  long  held  that  things  around  us,  animals, 
vegetables,  stones,  or  liquids,  partook  of  the  properties  of 
one  or  more  of  the  elements — Fire,  Air,  Earth,  or  Water. 
The  doctrine  was  a  very  ancient  one;  it  probably 
originated  in  India;  it  reached  our  forefathers  through 
the  Greeks.  Fire  was  supposed  to  be  '  hot  and  dry ' ;  air, 
'  hot  and  moist ' ;  water,  '  cold  and  moist ' ;  and  earth, 
'cold  and  dry.'  And  substances  which  partook  of  such 
qualities  were  supposed  to  contain  appropriate  amounts 
of  the  elements,  which  conferred  on  them  these  pro- 
perties. 

But  in  the  reign  of  Charles  n.  of  England,  about  the 
year  1660,  ^Robert  Boyle,  an  English  philosopher  and 
chemist,  restored  to  the  word  element  the  meaning  which 
its  derivation  implies.  '  Element,'  or  elemens  in  Latin,  is 
supposed  to  be  derived  from  the  three  letters  L  M  N ;  and 
to  denote  that,  as  a  word  is  composed  of  letters,  so  a  com- 
pound is  composed  of  elements.  Boyle,  in  his  celebrated 
work  The  Sceptical  Chymist,  restricted  the  use  of  the 
word  element  to  the  constituent  of  a  compound ;  and 
that  is  the  meaning  which  is  still  attached  to  the 
term. 

It  has  often  been  asked :  Does  a  compound  contain  an 
element  ?  Are  the  elements  actually  in  the  compound  ? 
If  this  means,  for  example,  that  iron  is  present  as  iron  in 

147 


148    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

iron-rust,  the  answer  must  be:  No.  The  properties  of 
rust  are  wholly  different  from  those  of  iron;  no  iron 
particle  can  be  detected  in  the  rust  by  any  tests  which  are 
suitable  for  the  recognition  of  the  metal  as  such.  But  if 
it  is  meant  that  iron  if  exposed  to  damp  air  changes  into 
rust,  and  that  by  suitable  treatment  metallic  iron  can  be 
extracted  from  rust,  then  the  answer  must  be  in  the 
affirmative. 

The  fact  that  an  element,  when  it  combines  with  other 
elements,  entirely  loses  its  original  properties,  led  to  the 
not  unnatural  supposition  that  it  should  be  possible  to 
change  an  element  into  another,  or  to  transmute  it.  Long 
before  the  notion  of  '  element '  was  formulated  by  Boyle, 
innumerable  attempts  had  been  made  to  convert  one 
metal  into  another ;  and,  indeed,  it  would  appear  on  the 
face  of  it  to  be  much  easier  to  transmute  lead  into  silver 
or  gold  than  to  convert  it  into  the  yellow  earthy  powder 
which  it  becomes  when  heated  in  air.  For  on  the  old 
doctrines,  the  properties  of  gold — its  lustre,  its  ductilit}7, 
its  melting  in  the  fire — were  much  more  similar  to  those 
of  lead  than  the  properties  of  litharge  or  oxide  of  lead, 
produced  by  heating  lead  to  redness  in  air.  After  Boyle's 
day,  however,  it  gradually  came  to  be  seen  that  certain 
substances  resisted  all  such  attempts  to  change  them  into 
others  without  increasing  their  weight.  For  example,  all 
changes  in  nature  not  of  a  temporary  and  evanescent  charac- 
ter which  iron  can  be  made  to  undergo,  are  accompanied 
by  an  increase  in  the  weight  of  the  iron ;  they  are  produced 
by  the  combination  of  iron  with  other  elements,  and  the 
addition  of  another  element  to  iron  invariably  increases 
the  weight,  for  the  weight  of  the  combining  element  is 
added  to  that  of  the  iron,  and  the  result  is  a  compound 
differing  in  properties  from  iron.  It  was  slowly  discovered 
that  about  seventy  substances  must  be  classed  as  elements 
— the  minimum  number  of  the  present  day  is  seventy- 


WHAT  IS  AN  ELEMENT  ?  149 

four — and  of  these  ten  are  gases,  two  are  liquids,  eight 
elements  are  usually  classed  as  non-inetals,  since  they  do 
not  possess  the  lustre  and  some  of  the  other  properties  of 
rnetals ;  and  the  remainder  are  metals.  These  substances 
are  classified  as  elements  solely  because  no  attempts  to 
convert  one  into  another  have  up  till  now  been  successful ; 
not  because  such  change  is  in  the  nature  of  things  im- 
possible. But  inasmuch  as  the  properties  of  these 
elements,  and  the  changes  which  they  undergo  on 
being  brought  together  with  other  elements  or  compounds, 
have  been  the  subject  of  an  enormous  number  of  experi- 
ments, and  because  no  hint  of  transmutation  has  been 
found,  the  conclusion  as  regards  the  immutability  of 
elements  has  been  arrived  at.  Hence  the  '  transmutation 
of  elements '  has  generally  been  regarded  as  impossible, 
and  as  unattainable  as  perpetual  motion,  or  as  the  '  quad- 
rature of  the  circle.' 

Speculation,  however,  has  a  deep  fascination  for  many 
minds ;  and  it  has  been  often  held  that  it  is  not  im- 
possible that  all  elements  may  consist  of  a  primal 
substance — 'protyle,'  as  it  has  been  called — in  different 
states  of  condensation.  It  will  be  worth  while  to  spend 
a  few  minutes  in  considering  the  reasons  for  this 
opinion. 

About  the  beginning  of  last  century,  John  Dalton 
revived  the  old  Greek  hypothesis  that  all  matter,  elements 
included,  consists  of  atoms  or  minute  invisible  particles ; 
these,  of  course,  like  the  matter  which  is  formed  of  them, 
possess  weight.  Although  they  are  so  minute  that  any 
attempt  to  determine  their  individual  weight  would  be 
out  of  the  question,  Dalton  conceived  the  idea  that  at 
least  their  relative  weights  could  be  determined,  by  ascer- 
taining the  proportions  by  weight  in  which  they  are  pre- 
sent in  their  compounds.  The  compound  of  hydrogen 
and  chlorine,  for  example,  commonly  known  as  muriatic 


150    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

or  hydrochloric  acid,  consists  of  one  part  by  weight  of 
hydrogen  combined  with  35J  parts  by  weight  of  chlorine ; 
and  as  it  is  believed  to  contain  one  atom  of  each  element, 
it  follows  that  an  atom  of  chlorine  is  35  J  times  as  heavy 
as  an  atom  of  hydrogen.  On  the  same  principle,  the 
relative  weights  of  the  atoms  of  other  elements  were 
determined.  And  so,  taking  the  weight  of  the  lightest 
atom,  hydrogen,  as  unity,  the  atom  of  nitrogen  weighs 
14  times  as  much,  of  oxygen  16,  of  iron  56,  of  lead  207, 
and  so  on. 

Attempts  to  classify  elements  according  to  their  proper- 
ties soon  followed ;  and  at  first  the  divisions  were  some- 
what arbitrary.  The  non-metals  were  distinguished  from 
the  metals  by  their  lack  of  lustre,  their  feeble  power  of 
conducting  heat,  and  the  fact  that  their  oxides  when 
mixed  with  water  generally  formed  acid  substances,  while 
those  of  the  metals  were  earthy,  insoluble  powders.  Cer- 
tain of  the  metals,  which  either  do  not  unite  with  or  are 
difficult  to  unite  with  oxygen  at  a  red  heat,  were  called 
'  noble '  metals ;  others,  which  are  at  once  attacked  by 
water,  such  as  sodium  and  potassium,  and  which  give 
soapy  liquids  with  a  harsh  taste,  were  named  '  metals 
of  the  alkalies/  and  so  with  the  rest.  In  1863,  however, 
Mr.  John  Newlands,  a  London  analyst,  was  successful  in 
arranging  the  elements  in  groups,  so  that  each  element 
in  a  horizontal  column  showed  analogy  with  others  in  the 
same  column.  He  found  that  by  writing  the  names  of 
the  elements  in  horizontal  rows,  beginning  with  the  one 
of  lowest  atomic  weight,  each  eighth  element  possessed 
properties  similar  to  those  of  the  elements  which  pre- 
ceded or  followed  it  in  the  vertical  columns.  And  in 
general  the  composition  of  the  compounds  of  such 
similar  elements  was  similar.  The  first  two  lines  of 
such  a  table  are  reproduced  here,  so  as  to  show  what  is 
meant : — 


WHAT  IS  AN  ELEMENT  ?  151 

Name     .    .     Lithium.  Beryllium.      Boron.       Carbon.      Nitrogen.      Oxygen.      Fluorine. 
Atomic  Weight  .7  9'1  11  12  14  16  19 

Name     .     .     Sodium.   Magnesium.   Aluminium.   Silicon.  Phosphorus.    Sulphur.  Chlorine. 

Atomic  Weight  .  23  24-4  2V1         28'4  31  32          35'5 

If  one  were  to  proceed  further  in  the  same  manner,  we 
should  find  five  elements  in  the  first  vertical  column — 
namely  lithium,  sodium,  potassium,  rubidium,  and 
caesium.  All  of  these  are  soft  metals,  easily  cut  with  a 
knife,  white  in  colour  like  silver,  rapidly  tarnishing  in  air, 
attacked  violently  by  water  so  that  they  either  catch  fire 
or  run  about  on  the  surface  of  the  water  and  rapidly  dis- 
appear. Their  compounds  with  chlorine  each  consist  of 
one  atom  of  each  element :  for  example,  using  Na 
(natrium)  as  the  symbol  for  one  atom  of  sodium,  and  Cl 
for  one  atom  of  chlorine,  the  composition  of  the  com- 
pound of  chlorine  with  sodium  (common  salt)  is  expressed 
by  the  formula  NaCI,  implying  that  the  compound  is 
formed  of  one  atom  of  each  element.  So  with  the 
others :  the  chloride  of  lithium  is  LiCl,  of  potassium 
KC1,  of  rubidium  RbCl,  and  of  cesium  CsCl.  They  all 
resemble  common  salt ;  the  taste  is  similar  in  all  cases, 
the  salts  dissolve  in  water,  they  are  all  white  in  colour, 
they  all  crystallise  in  cubes,  and  possess  many  other  pro- 
perties in  common.  The  oxides,  too,  are  all  powders, 
which  dissolve  in  water  and  give  liquids  with  a  soapy 
feel  and  a  burning  taste.  For  these  and  other  similar 
reasons,  all  these  elements  are  believed  to  belong  to  the 
one  class. 

Let  us  take  an  example,  too,  from  the  other  end  of  the 
table.  Fluorine,  the  first  of  the  column,  is  a  pale  yellow 
gas,  with  a  suffocating  odour.  It  combines  instantly  with 
hydrogen,  yielding  a  colourless  gas,  soluble  in  water,  and 
giving  an  acid  liquid,  which  corrodes  many  metals. 
Chlorine,  the  second  member,  is  a  greenish  yellow  gas, 
very  similar  in  properties  to  fluorine.  The  third  member, 


152    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

bromine,  is  a  dark  red  liquid,  but  at  a  somewhat  lower 
temperature  than  that  of  boiling  water  it  changes  into  a 
red  gas,  with  a  smell  similar  to  that  of  chlorine ;  iodine, 
though  a  black  solid  at  the  ordinary  temperature,  be- 
comes, when  heated,  a  violet  gas.  Like  fluorine,  they  all 
form  compounds  with  hydrogen,  of  the  formulse  HF,  HC1, 
HBr,  and  HI ;  these  are  colourless  gases,  soluble  in  water. 

Enough  has  been  said  to  show  that  Newlands'  method 
of  classifying  the  elements  brings  together  in  vertical 
columns  those  that  have  similar  properties.  This  method 
was  developed  by  a  German  chemist  named  Lothar 
Meyer,  and  by  a  Russian  named  Mendeleeff,  and  it  is  now 
universally  acknowledged  to  be  the  only  rational  way  of 
classifying  the  elements. 

If  we  consider  one  of  the  horizontal  rows,  we  shall  also 
discover  a  peculiarity.  The  number  of  atoms  of  the 
elements  which  combine  with  an  atom  of  oxygen  gradually 
alters ;  and  if  they  form  compounds  with  hydrogen,  the 
same  kind  of  regularity  can  be  observed.  For  instance, 
the  elements  of  the  first  horizontal  row  given  above  form 
the  following  compounds  with  oxygen  and  hydrogen : 

Name    .    .    Lithium.    Beryllium.     Boron.    Carbon.  Nitrogen.  Oxygen.  Fluorine. 
Formula  of 

.        Oxide .     .  Li20        BeO        B203      C02     N20fi 
Formula  of 

Hydride  .  LiH    unknown     BH3       CH4      NH3       OH2      FH 

The  elements  of  the  subsequent  rows  show  similar 
regularity. 

Up  till  recently,  no  elements  were  known  which  refused 
to  combine  with  other  elements.  In  1894,  however,  Lord 
Rayleigh  and  Sir  William  Ramsay  discovered  that 
ordinary  air  contained  such  a  gas,  and  they  named  it 
'argon,'  a  Greek  word  which  signifies  inactive  or  lazy. 
This  gas  had  been  overlooked  because  of  its  resemblance 
to  another  constituent  of  the  atmosphere,  present  in 
nearly  one  hundred  times  greater  amount — nitrogen. 


WHAT  IS  AN  ELEMENT  ?  153 

Argon  cannot  be  made  to  combine,  and  hence  it  is  left 
behind  when  the  nitrogen  and  oxygen  have  been  removed 
from  the  atmosphere. 

Shortly  after  the  discovery  of  argon,  Ramsay  found 
that  certain  minerals  when  heated  give  off  a  gas  similar 
to  argon,  inasmuch  as  it  forms  no  compounds,  but  with 
a  much  lower  atomic  weight;  for  while  argon  possesses 
the  atomic  weight  forty,  the  atomic  weight  of  helium  (the 
name  given  to  this  new  gas)  is  only  four.  Now  these 
elements  evidently  belong  to  one  series,  for  they  are  both 
colourless  gases,  incapable  of  combining  with  other 
elements.  And  it  appeared  almost  certain  that  other 
gases,  similar  in  properties  to  these  two,  should  be  capable 
of  existence.  And  Ramsay,  in  conjunction  with  Travers, 
spent  several  years  in  a  hunt  for  the  missing  elements. 
They  heated  upwards  of  a  hundred  minerals,  to  see 
whether  they  evolved  gas,  and,  if  so,  whether  the  gas 
obtained  was  new;  but  although  they  discovered  that 
many  minerals  give  off  helium  when  heated,  no  new  gas 
was  found.  Mineral  waters  were  boiled,  so  as  to  expel 
dissolved  gases ;  again  only  argon  and  helium  were 
obtained.  Even  meteorites,  or  '  falling  stars,'  were 
heated ;  only  one  was  found  to  give  off  gas  incapable  of 
combination,  and  that  gas  consisted  of  a  mixture  of  the 
two  which  were  already  known. 

As  a  last  attempt,  Ramsay  and  Travers  prepared  a  large 
quantity  of  argon,  by  removing  the  oxygen  and  the 
nitrogen  from  air,  and  then  forced  the  gas  into  a  bulb, 
dipping  in  a  vessel  immersed  in  a  tube  full  of  liquid  air, 
which  is  so  cold  that  the  argon  changed  to  liquid.  It 
forms  a  colourless,  mobile  liquid,  just  like  water.  When 
the  liquid  air  is  removed,  the  argon  begins  to  boil. 

It  was  hoped  that  the  distillation  of  crude  liquid  argon 
might  separate  from  it  other  gases  boiling  at  a  lower  or  a 
higher  temperature ;  that  if  it  contained  any  other  liquids 
of  lower  boiling-point,  these  would  distil  over  first,  and 


154    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

could  be  collected  separately;  while  any  'heavier'  gases 
would  be  the  last  to  distil  over*.  The  hope  was  not  dis- 
appointed— at  all  events  as  regards  the  first  expectation  ; 
for  the  first  part  of  the  gas  which  evaporated  was  consider- 
ably lighter  than  argon  and  had  a  much  lower  boiling- 
point.  After  a  few  redistillations,  however,  it  was  found 
that  liquid  air  was  not  sufficiently  cold  to  condense  this 
light  gas  to  liquid.  But  Dr.  Travers  was  equal  to  the 
emergency.  He  constructed  an  apparatus  by  help  of 
which  hydrogen  gas  was  condensed  to  liquid ;  and  the 
boiling-point  of  liquid  hydrogen  is  much  lower  than  that 
of  liquid  air;  it  is  —  252-5°  C.  On  cooling  the  mixture 
of  gases  which  had  been  separated  from  the  argon,  a 
portion  only  condensed,  while  about  one- third  still  remained 
as  a  gas ;  the  gaseous  portion  was  helium,  and  the  liquid  (or 
solid)  portion  evaporated  into  a  gas  which  was  named 
'  neon,'  the  Greek  word  for  '  new.' 

It  was  also  found  that  two  other  gases  could  be  sepa- 
rated from  air  by  allowing  a  large  quantity  of  liquid  air 
to  boil  away.  These  gases  have  a  much  higher  boiling- 
point  than  oxygen,  nitrogen,  or  argon,  and  therefore  they 
remain  mixed  with  the  last  drops  of  liquid  after  most  of 
the  air  has  evaporated.  They  were  separated  from  each 
other  by  ' fractionation ' ;  one  was  named  'krypton,'  the 
Greek  for  '  hidden ' :  and  the  other  '  xenon/  or  '  strange.' 

Five  new  gases  were  thus  obtained ;  they  are  given  with 
their  atomic  weight  in  the  following  line : 

Helium,  4 ;  Neon,  20  ;  Argon,  40  ;  Krypton,  81 '6  ;  Xenon,  128. 

Their  position  among  other  elements  is  well  seen  from  the 
following  extract  from  the  whole  table  of  the  elements : 

Hydrogen,  1  Helium,  4  Lithium,  7  Berylium,  9*1,  etc. 

Fluorine,  10  Neon,  20  Sodium,  23  Magnesium,  24'3,  etc. 

Chlorine,  35 '5  Argon,  40  Potassium,  39 '1  Calcium,  40,  etc. 

Bromine,  80  Krypton,  81  Rubidium,  85*4  Strontium,  87'6,  etc. 

Iodine,  127  Xenon,  128  Caesium,  133  Barium,  137'4,  etc. 


WHAT  IS  AN  ELEMENT  ?  155 

It  will  be  noticed  that  their  atomic  weights  lie  between 
those  of  the  elements  in*  the  vertical  rows ;  and  that  they 
separate  the  active  elements  of  the  fluorine  group  from 
the  equally  active  elements  of  the  sodium  group. 

The  discovery  of  these  elements,  however,  has  added 
little  to  our  knowledge  as  regards  the  nature  of  elements  in 
general,  except  in  so  far  as  to  show  that  elements  which 
form  no  compounds  can  exist.  It  might  be  supposed  that 
the  same  agencies  which  are  successful  in  splitting  up 
compounds  into  the  elements  of  which  they  consist  might 
decompose  elements  into  some  still  simpler  substances ; 
of  course  the  elements  thus  decomposed  could  no  longer 
be  called  elements.  And  it  appeared  not  impossible  that 
in  a  series  of  elements  closely  resembling  each  other,  like 
those  of  the  sodium  column,  or  the  chlorine  column,  it 
might  be  impossible  to  decompose  those  of  higher  atomic 
weight  into  those  of  lower  atomic  weight,  and  perhaps 
something  else.  Such  agencies  are :  a  high  temperature 
or  an  electric  current.  Water,  for  instance,  can  be  decom- 
posed into  hydrogen  and  oxygen  either  by  heating  steam 
to  whiteness  or  by  passing  an  electric  current  through 
water.  But  it  is  needless  to  say  that  the  elements  have 
been  repeatedly  exposed  to  the  highest  temperature  and 
to  the  strongest  electric  currents  and  yet  have  remained 
elements.  There  are,  indeed,  reasons  for  supposing  that 
at  the  enormously  high  temperatures  of  the  sun  and  of 
the  fixed  stars  some  of  our  elemei|j£  are  decomposed ;  but 
it  has  hitherto  been  impossible  to  reproduce  such  extreme 
conditions  on  the  earth. 

The  element  carbon  is  characterised  by  the  enormous 
number  of  compounds  which  it  forms,  chiefly  with  hydrogen 
and  oxygen,  although  many  other  elements  can  be  in- 
duced to  combine  with  it.  And  one  instructive  fact  is 
to  be  noticed  as  regards  such  compounds  :  the  greater  the 
number  of  atoms  they  contain  the  more  easily  they  are 


156    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

decomposed  by  heat.  Indeed,  some  compounds  are  so  un- 
stable that  they  decompose  at  the  ordinary  temperature, 
not  into  their  elements,  it  is  true,  but  into  other  com- 
pounds of  carbon,  hydrogen  and  oxygen.  Such  compounds 
are  stable  only  at  a  low  temperature,  and  the  higher  the 
temperature  the  more  readily  they  decompose.  Judging 
by  analogy,  we  should  expect  elements  of  high  atomic 
weight  to  show  tendency  to  decomposition,  granting,  of 
course,  that  any  element  at  all  is  capable  of  decomposing. 
Now  among  the  three  elements  of  highest  atomic  weight 
known  is  radium,  an  element  belonging  to  the  barium 
column,  of  which  the  atomic  weight  is  226.  This  remark- 
able substance  exists  in  a  mineral  named  pitchblende, 
an  oxide  of  uranium ;  its  discovery  by  Madame  Curie,  of 
Paris,  is  one  of  the  most  remarkable  of  recent  events  in 
chemical  history. 

The  second  element  of  high  atomic  weight  is  thorium 
(232'5).  It  was  noticed  by  Dr.  Schmidt,  and  indepen- 
dently by  Professor  Rutherford,  of  Montreal,  that  if  air 
was  passed  over  a  salt  of  thorium,  or  bubbled  through  its 
solution,  it  carried  with  it  an  '  emanation '  which  possessed 
for  a  short  time  the  power  of  discharging  an  electroscope. 
Radium  salts  also  give  off  such  an  emanation,  or  gas, 
which,  however,  retains  its  properties  for  more  days  than 
the  thorium  gas  does  for  minutes.  Uranium,  the  chief 
constituent  of  pitchblende,  too,  has  also  the  power  of 
discharging  an  electro^ope,  but  it  gives  off  no  emana- 
tion. Its.  atomic  weight  is  239'5 :  it  is  the  highest 
known. 

The  gases  evolved  from  compounds  of  thorium  and 
radium  can  be  condensed  to  solid  or  liquid  by  passing 
them  through  a  tube  cooled  with  liquid  air.  But  they 
are  present  in  such  excessively  minute  quantity  that  they 
have  never  been  seen,  even  as  a  minute  drop.  They  are 
as  inert  as  argon,  and  they  are  members  of  that  group  of 


WHAT  IS  AN  ELEMENT  ?  157 

elements ;  and  the  radium  gas  shines  in  the  dark,  so  that 
a  tube  containing  it  gives  off  a  whitish  phosphorescent 
light  like  that  given  off  by  stale  fish,  or  like  the  luminosity 
of  the  sea  on  calm  summer  evenings,  or  like  the  head  of  a 
lucifer  match  if  it  is  gently  rubbed  in  the  dark.  If  the 
gas  from  radium  is  mixed  with  air,  it  is  possible  to  see  it 
passing  through  a  tube  in  the  dark,  and  to  recognise  it  by 
its  faint  shining  when  it  is  transferred  from  one  glass  tube 
to  another. 

It  is  very  easy  to  remove  oxygen  from  a  mixture  of 
gases ;  if  a  piece  of  the  element  phosphorus  be  heated  in 
oxygen,  a  solid  compound  of  the  two  is  formed,  and  all 
oxygen  can  then  be  got  rid  of;  or  oxygen  may  be  ab- 
sorbed by  passing  the  mixed  gases  over  red-hot  copper. 
Hence  it  is  convenient  to  allow  the  emanation  from 
radium  salts  to  mix  with  oxygen  rather  than  with  air; 
for  nitrogen,  the  other  constituent  of  air,  is  more  diffi- 
cult to  remove.  And  it  is  then  possible  to  collect  the 
radium  emanation,  mixed  with  oxygen,  in  a  glass  tube, 
and  then  to  absorb  the  oxygen,  leaving  only  the  emana- 
tion present. 

Now,  as  has  been  said,  the  emanation  gradually  loses  its 
power  of  discharging  an  electroscope.  After  four  days  it 
requires  twice  as  much  emanation  to  produce  the  same 
discharging  effect  as  would  be  required  if  the  emanation 
were  freshly  prepared  from  radium  salts.  And  the  ques- 
tion suggested  itself  to  Mr.  Soddy  and  Sir  William  Ramsay : 
What  becomes  of  the  emanation  ?  Does  it  merely  lose  its 
luminosity  and  discharging  power,  or  is  it  changed  into 
something  else  ? 

Chemists  have  long  had  at  their  disposal  a  means  of 
recognising  almost  inconceivably  minute  quantities  of 
matter.  All  substances,  when  made  into  a  gas  by  intense 
heat,  give  out  light ;  and  that  light,  if  passed  through  a 
prism,  is  seen  not  often  to  be  all  of  one  kind.  For  example, 


158    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

the  light  given  out  by  sodium  gas  at  a  red  heat  is  yellow ; 
and  if  passed  through  a  slit,  and  then  through  a  prism, 
two  yellow  lines  are  seen — the  spectrum  of  sodium. 
Similarly,  potassium  salts,  in  a  spirit-lamp  flame,  gives 
out  a  violet  light ;  and  the  prism  shows  us  that  the  light 
consists  of  two  kinds — one  red  and  one  violet.  And  so 
for  other  elements.  If  the  spectra  of  gases  have  to  be 
examined,  they  can  be  made  to  glow  by  passing  an  electric 
discharge  through  a  very  narrow  tube  containing  a  minute 
trace  of  the  gas.  Helium,  for  example,  if  examined  in 
this  way,  gives  out  light  consisting  of  many  colours  :  red, 
yellow — the  most  intense — green,  green-blue,  blue  and 
violet.  Hence  it  is  easy  to  recognise  the  presence  of 
helium  in  such  a  capillary  tube,  by  passing  an  electric 
discharge  through  it,  for  the  exact  position  of  the  lines 
in  its  spectrum  is  easily  recognised. 

Now  Ramsay  and  Soddy  found  that  the  emanation  from 
radium  salts,  though  it  gave  out  a  special  light  of  its  own 
when  made  luminous  by  an  electric  discharge,  showed 
none  of  the  lines  characteristic  of  helium.  But  after 
standing  for  three  days  the  yellow  line  of  helium  began  to 
be  visible,  and  that  is  the  one  most  easily  seen.  As  time 
went  on,  and  as  the  emanation  lost  its  self-luminosity,  the 
other  lines  denoting  the  presence  of  helium  became  dis- 
tinctly visible.  The  conclusion  was  forced  upon  them, 
therefore,  that,  as  the  emanation  disappears,  helium  is 
formed,  or,  in.,  other  words,  the  emanation  is  changing 
slowly  into  helium. 

Professor  J.  J.  Thomson,  of  Cambridge,  has  of  recent 
years  been  investigating  the  motion  of  particles  which  are 
shot  off  from  the  negative  pole  when  an  electric  discharge 
is  passed  through  gases ;  and  he  has  succeeded  in  showing 
that  some  of  the  particles  move  with  enormous  rapidity, 
and  that  they  possess  a  weight  which  cannot  be  much 
more  than  one  seven-hundredth  of  that  of  a  hydrogen 


WHAT  IS  AN  ELEMENT?  159 

atom.  It  is  almost  certain  that  radium  salts  continually 
emit  such  rapidly  moving  particles,  and  it  is  known  that 
while  doing  so  the  temperature  of  the  radium  salt  is  some 
degrees  higher  than  that  of  the  surrounding  atmosphere ; 
radium,  therefore,  is  continually  giving  off  heat.  We  are 
wholly  unacquainted  with  any  similar  change;  these 
properties  are  new.  But  we  do  know  of  compound  sub- 
stances which  decompose  with  slight  provocation,  give  off 
a  great  amount  of  heat  in  doing  so,  and  at  the  same  time 
are  wholly  converted  into  a  large  quantity  of  gases ;  per- 
haps the  most  familiar  example  is  gun-cotton,  of  which 
most  of  the  high  explosives  used  for  blasting  and  in  the 
manufacture  of  modern  gunpowder  are  made.  The  dif- 
ferences between  the  two  phenomena,  moreover,  are 
sufficiently  pronounced:  gun-cotton  decomposes  almost 
instantaneously,  with  explosive  violence;  radium  salts 
slowly ;  gun-cotton  requires  to  be  started  by  the  explosion 
of  a  percussion-cap ;  radium  salts  decompose  spontaneously, 
and  the  rate  of  decomposition,  so  far  as  is  known,  appears 
to  be  independent  of  temperature;  the  amount  of  heat 
evolved  when  gun-cotton  explodes,  though  great  in  itself, 
is' small  in  comparison  with  that  evolved  during  the  de- 
composition of  an  equal  weight  of  radium  salt ;  and  it  is 
not  known  that  any  electrical  phenomena  accompany  the 
decomposition  of  gun-cotton.  Still,  it  appears  reasonable 
to  suspect  that  the  two  kinds  of  change  may,  after  all,  be 
similar,  and  that  the  heavy  atom  of  radium  is  decompos- 
ing into  the  lighter  helium  atom.  It  is  pretty  certain 
that  helium  is  not  the  only  substance  produced  when  the 
emanation  from  radium  decomposes;  and  it  is  not  known 
whether  radium,  when  it  gives  off  its  emanation,  produces 
at  the  same  time  any  other  decomposition  product.  Much 
has  yet  to  be  discovered.  Yet  it  must  be  acknowledged 
that  a  distinct  advance  has  been  made,  and  that  at  least 
one  so-called  element  can  no  longer  be  regarded  as  ulti- 


160    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

mate  matter,  but  is  itself  undergoing  change  into  a  simpler 
form  of  matter. 

The  young  student,  when  he  learns  what  is  known,  is 
too  apt  to  think  that  little  is  left  to  be  discovered ;  yet  all 
our  progress  since  the  time  of  Sir  Isaac  Newton  has  not 
falsified  the  saying  of  that  great  man — that  we  are  but 
children  picking  up  here  and  there  a  pebble  from  the 
shore  of  knowledge,  while  a  whole  unknown  ocean  stretches 
before  our  eyes.  Nothing  can  be  more  certain  than  this : 
that  we  are  just  beginning  to  learn  something  of  the 
wonders  of  the  world  on  which  we  live  and  move  and 
have  our  being. 


ON  THE  PERIODIC  ARRANGEMENT  OF 
THE  ELEMENTS 

AT  the  end  of  the  eighteenth  century,  after  the  investiga- 
tions of  Black,  Scheele,  Priestley,  Cavendish,  and  Lavoisier 
began  to  crystallise  the  previous  arbitrary  collections  of 
chemical  facts  into  more  or  less  of  a  system,  it  became 
evident  that  the  distinguishing  feature  of  a  '  compound/ 
as  contrasted  with  a  '  mixture,'  was  the  invariability  of  its 
composition.  Early  in  the  nineteenth  century,  Dalton 
formulated  his  celebrated  hypothesis,  by  means  of  which 
a  concrete  view  was  gained  regarding  the  cause  of  this 
constancy  and  invariability  of  composition.  Every  one 
knows  that  this  c  explanation '  consisted  in  the  supposition 
that  the  combination  of  two  substances,  one  with  another, 
in  definite  proportions,  involves  the  union  either  of  one 
atom  of  the  one  with  one  atom  of  the  other,  or  of  certain 
small  but  simple  numbers  of  atoms  of  the  two  substances. 
The  atom  was  regarded,  not  necessarily  as  indivisible,  but 
as  not  having  been  divided  into  any  smaller  particles. 
The  advance  made  by  Dalton  consisted  chiefly  in  ascribing 
to  each  atom  a  definite  weight ;  but  as  he  had  no  data  for 
determining  the  absolute  weight  of  any  one  atom,  he  was 
obliged  to  content  himself  with  relative  weights,  and  chose 
the  smallest  known  to  him,  that  of  hydrogen,  as  an  arbi- 
trary unit.  This  choice  has  proved  to  be  a  just  one,  for 
as  yet  no  element  has  been  discovered  possessing  a  lower 
atomic  weight  than  hydrogen,  although  it  is  by  no  means 
impossible  that  such  an  element  may  exist. 

L 


162    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

After  the  convenience  of  Dalton's  hypothesis  had  been 
acknowledged,  the  labour  of  chemists  was  for  many  years 
devoted  to  the  determination  of  the  relative  values  of  the 
'  atomic  weights '  of  the  elements ;  or,  expressed  in  a 
manner  independent  of  hypothesis,  of  their  combining 
proportions.  The  name  of  the  Swedish  chemist,  Berzelius, 
is  prominent  in  this  connection.  By  the  analysis  of  an 
almost  incredibly  large  number  of  compounds,  he  estab- 
lished on  a  firm  basis  the  constancy  of  composition  of 
compounds,  and  the  law  of  multiple  proportions.  Towards 
the  'forties,  therefore,  a  set  of  numbers  had  been  col- 
lected, which  invited  an  attempt  to  place  them  in  order, 
with  the  view  of  seeing  whether  some  still  more  profound 
law  could  not  be  discovered  connecting  the  combining 
numbers  attached  to  them.  Dobereiner,  as  early  as  1817, 
and  again  in  1829,  pointed  out  that  certain  elements  had 
atomic  weights  which  were  nearly  the  mean  of  those  of 
others  which  were  closely  related  to  them ;  thus,  the  mean 
of  the  atomic  weights  of  calcium  and  barium  gives  a  close 
approximation  to  the  atomic  weight  of  strontium  ;  that  of 
sodium  lies  near  the  mean  of  those  of  lithium  and  potassium; 
and  sulphur  and  tellurium  similarly  indicate  selenium 
as  a  middle  element.  In  1843  Gmelin,  who  published 
a  Handbook  of  Chemistry,  which  is  still  a  classic,  attempted 
a  classification  based,  not  upon  numerical  relations,  but 
on  similarity  of  properties.  For  instance,  we  find  the 
groups— F,  Cl,  Br,  I;  S,  Se,  Te;  P,  As,  Sb;  C,  B,  Si;  Li, 
Na,  K ;  Mg,  Ca,  Sr,  Ba ;  and  so  on.  In  1851  Dumas  gave 
a  lecture  before  the  British  Association,  in  which  he 
showed  that  not  merely  is  the  atomic  weight  of  bromine 
the  mean  of  those  of  chlorine  and  iodine,  but  that  its 
physical  properties,  such  as  its  colour,  its  density  in  the 
gaseous  and  in  the  liquid  state,  etc.,  are  also  half-way 
between  those  of  the  allied  elements.  In  1852  Faraday 
criticised  Dumas'  attempts  as  'speculations  which  have 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    163 

scarcely  yet  assumed  the  consistence  of  a  theory,  and 
which  are  only  at  the  present  time  to  be  ranked  among 
the  poetic  day-dreams  of  a  philosopher';  and  he  pro- 
ceeded :  '  We  seem  here  to  have  the  dawning  of  a  new  - 
light  indicative  of  the  mutual  convertibility  of  certain 
groups  of  elements,  although  under  conditions  which  are 
as  yet  hidden  from  our  scrutiny.' 

Passing  over  attempts  by  Gladstone,  Cooke,  Odling, 
and  Strecker,  we  come  to  the  years  1863  and  1864,  when 
John  Newlands,  in  a  series  of  letters  to  the  Chemical 
News,  announced  what  he  termed  the  '  Law  of  Octaves.' 
His  actual  words  were :  '  If  the  elements  are  arranged  in 
the  order  of  their  equivalents,  with  a  few  slight  trans- 
positions, it  will  be  observed  that  elements  belonging  to 
the  same  group  usually  appear  on  the  same  horizontal 
line.  It  will  also  be  seen  that  the  numbers  of  analogous 
elements  generally  differ,  either  by  7  or  by  some  multiple 
of  7 ;  in  other  words,  members  of  the  same  group  stand 
to  each  other  in  the  same  relation  as  the  extremities  of 
one  or  more  octaves  in  music.  Thus  in  the  nitrogen 
group,  between  nitrogen  and  phosphorus  there  are  7 
elements;  between  phosphorus  and  arsenic,  14;  between 
arsenic  and  antimony,  14 ;  and  lastly,  between  antimony 
and  bismuth,  14  also.  This  peculiar  relationship  I  propose 
provisionally  to  term  the  "  Law  of  Octaves." ' 

In  1869  and  1870,  Lothar  Meyer  and  Dmitri  Mendeleeff, 
independently  of  Newlands,  and  also  of  each  other, 
published  papers  in  which  they  maintained  that  the 
properties  of  the  elements  are  periodic  functions  of  their 
atomic  weights.  This  discovery  goes  by  the  name  of  the 
'Periodic  Law,'  or  better,  the  'Periodic  System.'  The 
arrangement  of  Meyer  (p.  164),  which  differs  but  little 
from  that  of  Mendeleeff,  is  the  one  generally  adopted. 

If  this  diagram  is  rolled  round  a  cylinder,  it  will  form  a 
continuous  spiral,  beginning  with  lithium  and  ending  with 


164    ESSAYS-BIOGRAPHICAL  AND  CHEMICAL 


I. 

II. 

III. 

IV. 

V. 

VI. 

VII."- 

^        VIII. 

Li 

He 

7-03 

Be 

f, 

9-1 

B 

11-0 

c 

12-0 

N. 

14-04 

0 

16-00 

F 

Na 

19 

Ne 

2305 

Mg 

20 

2436 

Al 

27-1 

Si 

28-4 

P 

31-0 

S 

32-06 

Cl 

K 

35-45 

A 

39-14 

Ca 

39-9 

40'0 

Sc 

44 

Ti 

48-1 

V 

51-2 

Cr 

521 

Mn 

Cu 

55-0 

Fe 

63-6 

Zn 

56-0 

Co 

Ni 

65-4 

Ga 

59-0 

58-7 

70 

Ge 

74 

As 

75 

Se 

79-1 

Br 

Rb 

79-96 

Kr 

85-4 

Sr 

81-5 

87-6 

Y 

89 

Zr 

90-6 

Nb 

94 

Mo 

96-0 

•t 

Ag 
107-95 

Cd 

99 

Ru 

101-7 

Rh 
103-0 

Pd 

106 

112 

In 

144 

Sn 

119-0 

Sb 

• 

120 

Te 

127-6 

I 

Cs 

126-85 

X 

133-0 

Ba 

1SS 

137-16 

La 

138 

Ce 

140 

Prd 

141 

Nd 

143-5 

V 

V 

152 

165 

9 

170 

Yb 

173 

9 

176 

Ta 

183 

W 

184 

1 

An 

185 

Os 

Ir 

Pt 

197-2 

Hg 

191 

193 

195-2 

200-3 

Tl 

204.1 

Pb 

206-9 

Bi 

208-5 

? 

210 

? 

? 

211 

\v    "V 

222 

Ra 

, 

o.v 

226 

^ 

i* 

230 

Th 

232 

V 

234 

U 

240 

? 

242 

PERIODIC  ARRANGEMENT  OF  ELEMENTS    165 

uranium ;  but  there  are  certain  gaps  unfilled,  denoted  by 
the  sign  ?,  which,  it  is  believed,  represent  the  places  of 
still  undiscovered  elements.  Indeed,  Meyer's  original 
diagram  contained  a  larger  number  of  these;  and  Men- 
deleeff,  averaging  the  properties  of  the  elements  surround- 
ing such  gaps,  prophesied  the  discovery  of  scandium, 
gallium,  and  germanium,  made  at  a  much  later  date  by 
Cleve,  by  Lecoq  de  Boisbaudran,  and  by  Winckler. 

There  are  many  other  ways  of  representing  these  rela- 
tions; but  except  perhaps  in  convenience  (and  questionably 
even  in  that),  they  present  no  particular  advantage,  and 
convey  no  new  knowledge.  Only  one  point  must  be 
emphasised.  The  elements,  as  arranged  above,  divide 
themselves  into  two  'periods' — long  periods  and  short 
periods.  Thus  the  seventh  member  after  lithium,  sodium, 
is  in  its  character  very  like  lithium;  and,  again,  potassium, 
the  seventh  after  sodium,  presents  strong  analogies  with 
the  two  elements  named ;  but  it  is  then  necessary  to  pass 
over  fifteen  elements  before  rubidium  is  reached,  which 
again  closely  resembles  lithium,  sodium,  and  potassium ; 
and  csBsium,  the  seventeenth  element  after  rubidium,  forms 
the  first  term  of  another  long  period.  Copper,  silver,  and 
gold  are  also  separated  by  long  periods ;  and  so  with  the 
elements  in  the  other  columns.  To  distinguish  these  in 
the  table,  the  symbols  of  the  elements  in  the  middle  of 
the  long  periods  are  printed  towards  the  left,  and  those  at 
the  beginning  towards  the  right,  of  the  figures  denoting 
the  atomic  weights. 

One  other  point  requires  mention.  Several  instances 
occur  in  which  the  elements  appear  to  occupy  a  reversed 
position.  Thus,  nickel,  with  the  atomic  weight  587, 
follows  cobalt,  to  which  a  higher  atomic  weight  is  ascribed; 
tellurium  precedes,  instead  of  following  iodine ;  and  it  will 
be  seen  that  argon  precedes  potassium.  The  differences 
between  the  various  consecutive  atomic  weights  are 


166    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

irregular,  and  vary  between  fairly  wide  limits ;  and  it  is 
quite  probable  that  these  differences  may  occasionally  be 
negative. 

In  1894  a  new  constituent  of  the  atmosphere,  which 
was  named  '  argon/  was  discovered  by  Lord  Rayleigh  and 
Ramsay;  this  was  followed  in  1895  by  the  discovery  by 
Ramsay  of  helium  in  certain  minerals.  This  gas  gives  a 
spectrum  in  which  a  brilliant  yellow  line  is  conspicuous. 
So  long  ago  as  1868  this  line  had  been  observed  in  the 
solar  spectrum  by  Jansen;  it  was  attributed  by  Frank- 
land  and  Lockyer  to  the  presence  of  a  new  element  in 
the  sun,  and  they  named  the  then  unknown  element 
'  helium.'  These  discoveries  were  followed  by  that  of  three 
other  gaseous  elements  in  atmospheric  air,  by  Ramsay  and 
Travers  in  1898;  thus  five  elements  were  added  to  the 
list.  All  these  elements  are  distinguished  by  their  inert- 
ness, for  none  of  them  forms  compounds  with  other 
elements. 

The  Roman  figures  at  the  head  of  the  columns  of  the 
periodic  table  have  a  certain  significance.  They  show  the 
maximum  number  of  atoms  of  hydrogen  which  the  ele- 
ments in  each  column  can  combine  with  or  replace,  or,  as 
it  is  termed,  their  'valency.'  Thus  an  atom  of  lithium 
combines  with  one  atom  of  hydrogen ;  it  can  also  replace 
one  atom,  as  when  it  forms  lithium  hydroxide,  LiOH,  in 
which  it  has  replaced  one  atom  of  hydrogen  in  water, 
H20.  So  also  magnesium  can  replace  two  atoms  of 
hydrogen,  for  it  forms  the  hydroxide  Mg(OH)2.  Boron 
combines  with  three  atoms  of  hydrogen;  carbon  with 
four;  phosphorus,  although  it  can  combine  with  only 
three  atoms  of  hydrogen,  can  replace  five ;  for  it  forms  a 
chloride  PC15,  in  which  it  has  replaced  the  five  atoms  of 
hydrogen  in  five  molecules  of  hydrogen  chloride,  5HC1. 
Sulphur  forms  a  hexafluoride,  and  iodine  a  pentafluoride, 
in  which  they  replace  six  and  five  atoms  of  hydrogen 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    167 

respectively,  in  6HF,  and  in  5HF.  Only  one  of  the  ele- 
ments of  the  eighth  group  appears  to  be  able  to  replace 
eight  atoms  of  hydrogen,  namely,  osmium ;  it  forms  a 
tetroxide,  Os04,  thus  replacing  the  eight  atoms  of  hydrogen 
in  four  molecules  of  water,  4H20.  But  the  new  gaseous 
elements  of  the  atmosphere  form  no  compounds,  and  have 
no  valency,  as  the  power  of  replacing  or  combining  with 
hydrogen  is  termed.  They  thus  form  a  column  by  them- 
selves; and  it  was  interesting  to  ascertain  whether  their 
atomic  weights  would  form  a  series  like  those  in  the  other 
columns.  In  this  case,  the  atomic  weight  could  not  be 
determined  by  the  usual  process  of  determining  the  ratio 
in  which  the  elements  combine  with  hydrogen ;  hence  a 
different  method  was  adopted,  depending  on  the  known 
fact  that  equal  numbers  of  molecules  of  gases  occupy 
equal  volumes  under  the  same  conditions  of  temperature 
and  pressure ;  and  making  use  of  an  argument  relating  to 
the  number  of  atoms  in  such  molecules.  The  atomic 
weights  were : — 


Helium 

4 

Neon 
20 

Argon 
39-9 

Krypton 
81-5 

Xenon 
128 

These  numbers,  as  will  be  seen  on  reference  to  the  table, 
fit  in  the  eighth  column ;  the  symbols  and  atomic  weights 
of  these  gases  are  printed  in  italics.  They  form  the  initial 
members  of  the  first  and  second  short  series,  and  of  the 
first,  second,  and  third  long  series. 

Some  doubt  exists  as  to  the  place  to  be  assigned  to 
hydrogen,  the  element  with  lowest  atomic  weight.  Both 
Mendeleeff  and  Meyer  shirked  placing  it.  It  may  be  that 
it  should  be  placed  at  the  head  of  the  fluorine  column ; 
but  there  are  equally  good,  or  perhaps  better,  reasons  for 
believing  that  it  is  the  first  member  of  the  lithium 
column. 


168    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Many  attempts  have  been  made  to  devise  some  mathe- 
matical relation  between  these  atomic  weights.  So  long 
as  there  was  reason  to  doubt  the  accuracy  of  the  experi- 
ments by  means  of  which  the  atomic  weights  have  been 
determined,  some  such  relation  as  the  following  had 
considerable  probability  in  its  favour  :  —  Taking  the 
differences  between  the  atomic  weights  of  the  elements 
in  the  first  column,  lithium,  sodium,  potassium,  rubidium, 
and  caesium,  they  are  — 


K-Na  =  39-23  =  16; 

Rb-K  =  85-39  =  46  =  (3xl6)  nearly; 

Cs-Rb  =  133-85  =  48  =  (3xl6). 

The  differences  are  16,  16,  3x16,  and  3x16.  Now 
there  are  compounds  of  carbon  and  hydrogen  which 
possess  the  formulae,  CH4,  C2H6,  C3H8,  C4H10,  C5H12,  C6H14, 
etc.  ;  and  as  the  atomic  weight  of  carbon  is  12,  and  that  of 
hydrogen  1,  the  sum  of  the  atomic  weights,  or,  as  they  are 
called,  the  molecular  weights,  are  respectively  16,  30,  44, 
58,  72,  86,  etc.,  with  a  common  difference  of  14.  We  see, 
therefore,  that  a  set  of  compounds  may  so  differ  in  mole- 
cular weight  as  to  present  a  regular  series,  with  a  common 
difference.  Nothing  was  more  likely,  then,  than  that 
sodium  should  be  regarded  as  a  compound  of  one  atom  of 
lithium  with  one  atom  of  an  unknown  element  of  atomic 
weight  16,  or  with  two  atoms  of  an  unknown  element  of 
atomic  weight  8  ;  while  potassium  might  be  looked  upon 
as  a  compound  of  an  atom  of  lithium,  with  four  atoms  of 
the  element  of  atomic  weight  8  ;  and  so  on.  But,  unfor- 
tunately for  this  simple  theory,  the  differences  between 
the  atomic  weights  of  the  elements  are  not  exactly  equal. 
Instead  of  16,  the  real  difference  between  the  atomic 
weights  of  lithium  and  sodium  is  16  '02;  between  potassium 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    169 

and  sodium,  16'09;  and  so  on.  In  other  groups  the 
divergences  are  still  more  striking. 

The  cause  of  this  Jrregularity  has,  therefore,  to  be 
sought.  In  seeking  for  a  clue,  the  first  question  is :  Are 
the  atomic  weights  invariable  ?  A  further  question  is :  Is 
weight  invariable  ?  Does  a  body  always  possess  the  same 
weight  under  all  conditions  ?  For  example,  would  the 
weight  of  a  body  remain  the  same  if  it  were  to  be  weighed 
at  different  temperatures?  Or,  if  electrically  charged, 
would  its  weight  remain  unaltered  ? 

It  is  a  very  difficult  problem  to  weigh  an  object  at  a 
high  temperature.  If  the  balance,  as  is  usual,  contains 
air,  convection  currents  are  produced  by  the  ascent  of  air 
heated  by  the  warm  body,  and  the  body  apparently  weighs 
too  little.  If  the  whole  balance  were  uniformly  heated, 
the  weights  would  be  at  the  same  temperature  as  the 
substance  weighed ;  and  it  is  to  be  presumed  that  both 
they  and  the  substance  would  alter  in  weight  equally,  and 
still  remain  in  counterpoise.  And  if  the  balance  case  be 
pumped  empty  of  air,  as  was  done  by  Crookes  in  deter- 
mining the  atomic  weight  of  thallium,  other  phenomena 
intervene,  which,  however  interesting  in  themselves  (they 
led  Crookes  to  the  invention  of  the  radiometer),  are  very 
disconcerting ;  for  attractions  and  repulsions,  which  com- 
pletely disturb  equilibrium,  are  produced  by  the  slightest 
variations  of  temperature.  However,  some  curious  calcula- 
tions have  been  made  by  Hicks  in  dealing  with  Baily's 
experiments  on  the  attraction  of  leaden  balls  by  masses 
of  lead — experiments  which  afford  data  for  calculating  the 
density  of  the  earth.  At  a  high  temperature  the  attraction 
appeared  to  be  less  than  at  a  low  one ;  and  as  the  attrac- 
tion of  the  earth  is  the  cause  of  weight,  supposing  these 
experiments  to  be  correct,  and  the  deductions  legitimate, 
it  would  follow  that  weight  is  altered  by  temperature. 
The  subject  is  well  worthy  of  further  experiment. 


170    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

Again,  interesting  experiments  have  been  made  by 
Landolt  as  regards  constancy  of  weight.  Having  sealed 
up  in  an  inverted  U-tube  two  substances  capable  of  acting 
on  each  other,  such  as  silver  nitrate  and  sodium  chloride, 
each  substance  in  solution  occupying  one  limb  of  the 
tube,  he  weighed  the  tube  with  the  utmost  accuracy ;  the 
possible  error  might  be  one  part  in  a  million.  On  inverting 
the  tube,  the  two  solutions  mixed,  and  the  reaction  took 
place.  It  was  again  weighed.  For  long,  Landolt  supposed 
that  he  had  detected  small  changes  in  weight,  sometimes 
negative,  sometimes  positive;  but  he  was  able  to  trace 
these  changes  to  the  porous  nature  of  glass.  On  employ- 
ing tubes  made  of  fused  quartz,  no  change  of  weight  could 
be  detected  after  the  reaction  was  over.  Apparently, 
therefore,  no  change  of  weight  takes  place  as  the  result  of 
a  chemical  reaction,  provided  nothing  leaves  or  enters  the 
vessel  in  which  the  reaction  goes  on. 

A  very  ingenious  experiment  of  Joly's  deserves  mention. 
It  was  designed  to  try  whether  any  change  of  mass  occurs 
on  mixing  two  reacting  bodies,  and  the  disposition  of  the 
apparatus  was  somewhat  like  that  devised  by  Landolt. 
But  instead  of  utilising  the  attraction  of  the  earth  in  order 
to  estimate  whether  the  mass  had  changed  or  not,  the 
inertia  of  the  substances  and  of  their  mixture  was  deter- 
mined. The  vessel  containing  the  substances  to  be  mixed 
was  suspended  to  the  arm  of  a  torsion-balance,  the  arm  of 
which  was  at  right  angles  to  the  direction  of  motion  of  the 
earth,  which  is  known  to  be  at  the  rate  of  about  30  miles 
a  second  through  space.  If  matter  had  been  created 
during  the  chemical  change,  then  the  created  matter 
would  not  partake  of  the  earth's  velocity,  and  a  retarda- 
tion, made  manifest  by  the  rotation  of  the  arms  of  the 
torsion-balance  in  one  direction,  would  have  been  observed ; 
and. if,  on  the  other  hand,  matter  had  been  destroyed,  an 
acceleration  would  have  shown  itself.  The  experiments 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    171 

were  entirely  negative ;  hence  it  may  be  concluded,  con- 
firmatory of  the  experiments  of  Landolt,  that  no  change 
in  mass  is  produced  by  a  chemical  reaction.  A  variation 
in  weight  or  in  inertia  has  not  been  observed. 

There  is  one  curious  discrepancy  which  still  remains 
unexplained.  The  density  of  nitrogen  gas  has  been  very 
accurately  determined  by  two  very  competent  observers — 
Lord  Rayleigh  and  Leduc.  They  both  agree  in  their 
results  to  one  part  in  10,000.  Now  it  is  known,  for  reasons 
into  which  we  cannot  enter  here,  that  the  molecules  of 
both  nitrogen  and  oxygen  consist  each  of  two  atoms ;  and 
as  it  is  also  certain  that  equal  volumes  of  gases  contain 
nearly  equal  numbers  of  molecules,  when  measured  under 
similar  conditions  of  temperature  and  pressure,  the  rela- 
tive weights  of  these  gases  correspond  to  the  relative 
weights  of  the  atoms.  The  word  '  nearly '  has  been  used ; 
for  a  slight  correction  must  be  introduced  in  order  to 
secure  exact  correspondence.  Hence  the  atomic  weight 
of  nitrogen,  referred  to  that  of  oxygen  taken  as  16,  as  is 
now  customary,  must  be  14r008,  since  that  is  the  density  of 
nitrogen  referred  to  oxygen  as  16,  after  the  necessary  cor- 
rection has  been  made.  But  this  number  does  not  corre- 
spond with  the  atomic  weight  of  nitrogen  obtained  by  the 
celebrated  chemist  Stas,  as  the  result  of  the  analysis  of  such 
compounds  as  potassium  nitrate,  when  he  determined  the 
ratio  between  the  quantities  of  nitrogen  and  oxygen  in 
the  molecule  KN03.  Both  he  and,  quite  recently,  one 
of  the  most  skilful  of  analysts,  to  whom  we  owe  in  recent 
years  many  exact  determinations  of  atomic  weights, 
Theodore  Richards,  agreed  in  ascribing  the  number  14'04 
to  nitrogen  as  its  atomic  weight.  The  difference  does  not 
appear  very  great ;  but  yet  it  amounts  to  one  part  in  370 : 
and  the  error  of  experiment  is  not  likely  to  be  greater 
than  one  part  in  10,000.  This  discrepancy  is  one  of.  the 
most  curious  of  chemical  facts,  and  it  would  well  repay 


172    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

further  investigation.  It  may  be  added  that  the  deter- 
mination by  Gray  of  the  density  of  nitric  oxide,  a  com- 
pound containing  one  atom  of  nitrogen  in  combination 
with  one  atom  of  oxygen,  entirely  corroborates  the  results 
of  Lord  Rayleigh  and  Leduc.  Experiments  are  now  in 
progress  to  combine  a  weighed  quantity  of  nitric  oxide 
with  oxygen,  so  as  to  cause  it  to  take  up  one  other  atom 
of  oxygen,  and  to  find  the  increase  in  weight ;  and  also 
to  remove  from  it  the  atom  of  oxygen,  and  to  find  the 
weight  of  the  oxygen  removed ;  we  may,  therefore,  hope 
for  some  explanation  of  the  above  discrepancy  at  no  dis- 
tant date.1 

The  writer  of  this  article  was  so  much  impressed  by  the 
consideration  of  this  discrepancy,  that  some  years  ago,  in 
conjunction  with  Miss  Aston,  an  attempt  was  made  to 
find  whether  the  fact  of  a  compound  having  been  formed 
with  absorption,  instead  of,  as  is  commoner,  with  evolu- 
tion of  heat,  had  any  influence  on  the  proportions  of  the 
elements  which  it  contained.  For  this  purpose  the  salts 
of  a  curious  acid  derivative  of  nitrogen  named  hydrazoic 
acid,  HN3,  were  analysed ;  but  there  is  reason  to  distrust 
the  results,  for  it  is  possible  that  decomposition  occurred 
during  the  preparation  to  some  small  extent,  and  so  may 
not  have  led  to  trustworthy  conclusions.  But  such  as 
they  were,  they  were  in  favour  of  the  supposition  that  the 
atomic  weight  of  nitrogen  in  such  compounds  is  less  than 
in  those  formed  with  evolution  of  heat,  like  the  nitre 
analysed  by  Stas  and  by  Richards. 

An  entirely  new  light  has  been  thrown  on  the  numerical 
relations  of  the  atoms  by  the  remarkable  discovery  of 
radium  by  the  Curies,  and  by  the  discovery  by  Rutherford 
and  Soddy,  that  what  are  termed  the  '  rays '  from  its  salts, 

1  Such  investigations  have  since  been  carried  out  by  Dr.  R.  Gray  and 
by  Professor  Philippe  Guye,  with  the  result  that  the  true  atomic  weight 
of  nitrogen  has  been  fixed  as  14*01. 


Y   I 

OF 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    173 

as  well  as  from  those,  of  thorium,  are  produced  by  gases 
resembling  in  their  inertness  the  gases  of  the  argon  group. 
These  gases,  moreover,  have  the  extraordinary  property 
that  they  are  transient,  although  they  change  in  very 
different  intervals  of  time.  Whereas  the  gas  from  thorium 
is  half  gone  in  about  a  minute  (that  is,  has  changed  to 
the  extent  of  one-half  into  some  other  substance  or  sub- 
stances), that  from  radium  requires  about  four  days  before 
it  has  undergone  half  the  change  of  which  it  is  capable. 
A  third  gas  has  been  obtained  from  a  radio-active  element 
to  which  the  name  '  actinium '  has  been  given  by  its  dis- 
coverer, Debierne;  this  gas  has  an  extraordinarily  short 
life,  for  the  total  duration  of  its  existence  is  only  a  few 
seconds.  The  spectrum  of  the  gas  from  radium  has  been 
mapped  by  Ramsay  and  Collie ;  the  amount  of  gas  pro- 
duced from  a  known  weight  of  radium  bromide  has  been 
measured  by  Ramsay  and  Soddy;  and  they,  too,  proved 
that  one  of  its  products  of  decomposition  is  the  lightest 
gas  of  the  argon  group,  helium.  At  first,  the  spectrum  of 
the  emanation  from  radium  shows  none  of  the  character- 
istic lines  of  helium ;  but  in  the  course  of  a  few  days  the 
helium  spectrum  appears  in  full  brilliancy.  Here,  evi- 
dently, is  a  case  of  the  transformation  of  one  element  into 
another ;  no  doubt  there  are  other  products  than  helium, 
but  what  they  are  remains  for  the  present  unknown.  If 
they  were  elements  like  iron,  for  example,  there  are  at 
present  no  known  means  delicate  enough  to  detect  the 
extremely  minute  amount  which  would  be  produced. 
These  gases  from  radium,  thorium,  and  actinium  are  self- 
luminous,  and  shine  brilliantly  in  the  dark ;  and  they  also 
possess  the  power  of  altering  air  and  other  gases  with 
which  they  are  mixed,  so  that  they  acquire  the  property 
of  discharging  an  electrified  body;  the  air  is  said  to  be 
'  ionised.'  But  a  still  more  remarkable  property  is  their 
giving  off  heat  during  their  change  into  other  elements, 


174    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

the  amount  of  heat  being  enormous  when  their  extremely 
small  quantity  is  considered.  Thus  the  radium  emana- 
tion (the  name  applied  to  the  gas  which  is  continuously 
evolved  from  salts  of  radium),  during  its  decomposition 
gives  off  no  less  than  three  million  times  the  heat  which 
would  be  evolved  during  the  explosion  of  an  equal  volume 
of  a  mixture  of  oxygen  and  hydrogen  in  the  proportion 
requisite  to  form  water.  Now  if  radium  is  disappearing, 
it  must  be  continually  in  process  of  formation,  else  there 
would  be  none  on  the  surface  of  the  earth ;  it  would  all 
have  disappeared  and  have  been  changed  into  other 
bodies  during  the  lapse  of  time  since  the  minerals  con- 
taining it  were  formed.  As  radium  is  always  associated 
with  uranium,  it  appears  not  unreasonable  to  suppose  that 
uranium,  too,  which  is  a  radio-active  element,  is  slowly 
changing  into  radium ;  and  there  appears  to  be  definite 
ground  for  the  surmise  that  polonium,  the  first  of  the 
radio-active  elements,  also  discovered  by  Madame  Curie, 
which  has  a  half-life  period  of  about  one  year,  is  a  product 
of  the  decomposition  of  radium,  with  which  it  is  always 
associated.  It  may  be  mentioned,  too,  that  all  minerals 
containing  uranium  contain  more  or  less  helium. 

It  will  be  noticed,  on  referring  to  the  periodic  table, 
that  all  the  radio-active  elements,  that  is,  all  those  which 
are  undergoing  change  of  the  nature  described,  have  very 
high  atomic  weights.  That  of  uranium  is  240;  that  of 
thorium,  232  ;  and  that  of  radium,  226.  Now  it  is  a  com- 
monplace of  the  organic  chemist  that  it  is  not  possible  to 
build  up  compounds  of  carbon  and  hydrogen  of  unlimited 
complexity;  indeed,  it  is  doubtful  if  any  compound  has 
been  prepared  containing  more  than  100  atoms  of  carbon. 
Attempts  to  prepare  them  lead  to  failure,  owing  to  their 
decomposing  at  the  ordinary  temperature  into  compounds 
containing  a  smaller  number  of  atoms.  And  it  is  pro- 
bable that  more  complex  hydrocarbons,  as  such  com- 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    175 

pounds  are  termed,  would,  if  they  could  exist,  decompose 
with  evolution  of  heat.     Such  a  decomposition  appears  to 
present  analogy  with  the  change  which  an  element  like 
radium  is  undergoing.     It  is  in  process  of  change  into 
other  elements  of  lower  atomic  weight ;  and  in  changing, 
it  evolves  heat,  in  amount  enormously  greater  than  that 
produced  by  any  change  of  a  compound  into  a  mixture  of 
simpler  compounds.     But  the  matter  is  complicated  by 
another  phenomenon — that   of  discharging  with  almost 
inconceivable  velocity  particles  which  appear,  according 
to  J.  J.  Thomson,  to  be  identical  with  negative  electricity. 
These  '  corpuscles/  as  they  have  been  termed,  embed  them- 
selves in   the  vessel  in  which  the  radio-active  body  is 
confined ;  and,  owing  to  their  extreme  minuteness,  they 
may  even  pass  through  the  walls  of  the  containing  vessel. 
Indeed  the  opposition  of  their  passage  has  been  shown  to 
depend  merely  on  the  density  of  the  matter  of  which  the 
confining  walls  are  composed ;  gold,  which  is  denser  than 
lead,  stops  their  passage  better  than  lead;  for  a  similar 
reason  lead  is  better  than  iron,  iron  better  than  glass,  and 
so  on.    Thomson  has  calculated  that  the  mass  of  one  such 
particle  is  approximately  one-thousandth  of  that  of  an 
atom  of  hydrogen. 

This  new  chemistry  is  just  at  its  commencement.  It 
dates  from  1896,  when  Becquerel  showed  that  compounds 
of  uranium  evolved  some  sort  of  radiation  which  would 
impress  a  photographic  plate.  It  is  still  too  early  to 
formulate  any  definite  statement  relating  to  its  connection 
with  the  irregularity  in  the  numerical  sequence  of  the 
atomic  weights ;  yet  it  may  be  permissible  to  speculate, 
aided  by  the  recent  discoveries.  When  two  elements 
combine,  heat  is  generally  evolved ;  now  heat  is  only  one 
form  of  energy,  and  the  combination  of  elements  may  be 
so  carried  out  as  to  be  accompanied  by  other  kinds  of 
energy — for  instance,  by  the  production  of  an  electric. 


176    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

current.  Conversely,  when  a  compound  is  resolved  into 
its  elements,  it  is  generally  necessary  to  impart  energy  to 
it ;  and  the  element  may,  therefore,  be  said  to  '  contain ' 
more  energy  than  its  compounds.  Now,  as  Ostwald  has 
pointed  out  in  his  'Faraday'  lecture,  the  progress  of 
discovery  has  kept  pace  with  the  amount  of  energy  with 
which  it  was  possible  at  the  time  to  load  a  compound; 
and  he  cited  the  discovery  of  the  metals  of  the  alkalies, 
sodium  and  potassium,  by  Davy.  It  was  because  Davy 
had  at  his  disposal  the  powerful  battery  of  the  Royal 
Institution,  that  he  was  able  to  convey  enough  energy 
into  caustic  potash  to  isolate  from  it  potassium,  hydrogen, 
and  oxygen.  If  we  assume  that  radium,  as  may  be 
possible,  is  produced  by  a  spontaneous  change  in  uranium ; 
and  if  we  also  assume  that  radium  contains  more  energy 
than  uranium ;  then  as  such  a  spontaneous  change  must 
be  accompanied,  on  the  whole,  by  a  loss  of  energy,  there 
must  be  formed  other  bodies  from  the  uranium  which 
contain  less  energy  than  it  does.  Such  a  substance  may 
be  iron,  which  is  generally  found  in  company  with  uranium. 
If  we  could  concentrate  energy  into  iron,  it  might  be 
possible  to  convert  it  into  uranium. 

But  there  is  another  side  to  this  question.  The  nature 
of  the  energy  required  appears  to  be  electric  in  character. 
Now  it  is  almost  certain  that  negative  electricity  is  a 
particular  form  of  matter;  and  positive  electricity  is 
matter  deprived  of  negative  electricity— that  is,  minus  this 
electric  matter.  The  addition  of  matter  in  any  form  would, 
according  to  all  experience,  increase  mass ;  it  would  also  in- 
crease weight.  It  is,  therefore,  conceivable  that  an  element 
may  consist  of  a  compound  of  two  or  more  elements  of 
lower  atomic  weight,  plus  a  certain  quantity  of  negative 
electricity.  This  might  account  for  the  approximate 
numerical  relations  which  subsist  between  the  atomic 
weights  of  the  nearly  related  elements ;  and  also  for  the  fact 


PERIODIC  ARRANGEMENT  OF  ELEMENTS    177 

that  the  relation  is  not  an  exact  one,  but  only  approximate ; 
for  the  difference  between  the  actual  atomic  weight,  and 
that  which  would  follow  if  one  element  were  a  compound 
of  other  elements  of  lower  atomic  weights,  would  be  caused 
by  the  addition  of  a  certain  number  of  electric  atoms  to 
the  molecule. 

It  must  be  confessed,  however,  that  the  basis  for  specu- 
lations like  these  is  a  slender  one ;  the  sole  ground  is  the 
undoubted  fact  that  radium  produces  an  emanation 
which  spontaneously  changes  into  helium ;  and  also  that, 
in  doing  so,  the  emanation  parts  with  a  large  number 
of  corpuscles  carrying  negative  charges.  Nevertheless, 
enough  is  known  to  prove  that  there  is  a  wide  field  for 
experiment,  and  that  the  harvest  will  be  a  rich  one; 
further,  the  reapers'  task  will  be  one  of  extraordinary 
interest. 


RADIUM  AND  ITS  PRODUCTS 

CHEMISTRY  and  physics  are  experimental  sciences;  and 
those  who  are  engaged  in  attempting  to  enlarge  the 
boundaries  of  science  by  experiment  are  generally  un- 
willing to  publish  speculations ;  for  they  have  learned,  by 
long  experience,  that  it  is  unsafe  to  anticipate  events.  It 
is  true  they  must  make  certain  theories  and  hypotheses. 
They  must  form  some  kind  of  mental  picture  of  the 
relations  between  the  phenomena  which  they  are  trying 
to  investigate,  else  their  experiments  would  be  made  at 
random  and  without  connection.  Progress  is  made  by 
trial  and  failure;  the  failures  are  generally  a  hundred 
times  more  numerous  than  the  successes;  yet  they 
are  usually  left  unchronicled.  The  reason  is  that  the 
investigator  feels  that  even  though  he  has  failed  in 
achieving  an  expected  result,  some  other  more  fortunate 
experimenter  may  succeed,  and  it  would  be  unwise  to 
discourage  his  attempts. 

In  framing  his  suppositions,  the  investigator  has  a 
choice  of  five  kinds;  they  have  been  classified  by  Dr. 
Johnstone  Stoney.  '  A  theory  is  a  supposition  which  we 
hope  to  be  true,  a  hypothesis  is  a  supposition  which  we 
expect  to  be  useful ;  fictions  belong  to  the  realm  of  art ;  if 
made  to  intrude  elsewhere,  they  become  either  make- 
believes  or  mistakes/  Now  the  '  man  in  the  street/  when 
he  thinks  of  science  at  all,  hopes  for  a  theory ;  whereas 
the  investigator  is  generally  contented  with  a  hypothesis, 
and  it  is  only  after  forming  and  rejecting  numerous  hypo- 

179 


180    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

theses  that  he  ventures  to  construct  a  theory.  He  has  a 
rooted  horror  of  fiction  in  the  wrong  place,  and  he  dreads 
lest  his  hypothesis  should  turn  out  to  be  misplaced 
fiction. 

I  have  thought  it  better  to  begin  by  these  somewhat 
abtruse  remarks,  in  order  to  place  what  I  propose  to 
discuss  on  a  true  basis.  It  is  to  be  understood  that  any 
suppositions  which  I  shall  make  use  of  are  of  the  nature 
of  hypotheses,  devised  solely  because  they  may  prove 
useful.  Events  are  not  yet  ripe  for  a  theory. 

It  will  be  remembered  that  Professor  Rutherford  and 
Mr.  Soddy  announced  a  '  view '  that  certain  elements 
which  possess  the  power  of  discharging  an  electroscope, 
and  which  are  therefore  called  '  radioactive/  are  suffering 
disintegration — that  is,  they  are  splitting  up  into  other 
elements,  only  one  of  which  has  as  yet  been  identified. 
Three  of  these  elements,  namely,  radium,  thorium,  and 
actinium,  early  in  the  process  of  disintegration  give  off  an 
'  emanation,'  or  supposed  gas ;  the  proof  of  the  gaseous  nature 
of  these  emanations  is  that  they  can  be  confined  by  glass 
or  metal,  like  gases,  and  that  they  can  be  liquefied  or 
solidified  when  cooled  to  a  sufficiently  low  temperature. 
It  is  necessary  to  pay  attention  to  this  peculiarity;  for 
these  radioactive  elements,  and  two  others,  uranium  and 
polonium,  also  give  off'  so-called  /3-rays,  which  penetrate 
glass  and  metal,  and  which  are  believed  from  the  dis- 
coveries of  Professor  J.  J.  Thomson  and  others  to  be 
identical  with  negative  electricity. 

Now  Rutherford  and  Soddy,  reasoning  on  the  premises 
that  radium  was  always  found  associated  with  uranium 
and  thorium,  and  also  that  the  ores  of  these  metals, 
pitchblende  and  thorite,  had  been  found  to  contain  the 
gas  helium,  made  the  bold  suggestion,  '  The  speculation 
naturally  arises  whether  the  presence  of  helium  in  minerals 
and  its  invariable  association  with  thorium  and  uranium 


RADIUM  AND  ITS  PRODUCTS  181 

may  not  be  connected  with  their  radioactivity.'  Besides 
the  premises  already  mentioned,  they  had  evidence  of 
the  probable  mass  of  the  '  a-particles,'  which  appeared  to 
be  about  twice  that  of  an  atom  of  hydrogen.  Now 
helium  is  the  lightest  gas  next  to  hydrogen;  and  its 
atoms  are  four  times  as  heavy  as  atoms  of  hydrogen.  It 
was,  therefore,  a  striking  confirmation  of  the  accuracy  of 
this  view  when  Ramsay  and  Soddy  discovered  that  helium 
can  actually  be  obtained  from  radium. 

Before  giving  an  account  of  that  discovery,  a  short 
description  of  the  nature  and  properties  of  helium  may 
not  be  out  of  place.  When  light  passes  through  a  prism, 
it  is  refracted  or  bent ;  and  Newton  discovered  that  white 
light,  such  as  is  emitted  from  the  sun  or  the  stars,  after 
passing  through  a  prism,  gives  a  spectrum  consisting  of 
coloured  images  of  the  hole  in  the  window-shutter  through 
which  the  sunlight  fell  on  his  prism.  Fraunhofer,  a 
Berlin  optician,  conceived  the  idea  of  causing  the  light  to 
pass  through  a  narrow  slit,  instead  of  a  round  hole ;  and 
the  spectrum  then  consisted  of  a  number  of  images  of  the 
narrow  slit,  instead  of  the  round  hole.  He  was  struck  by 
one  peculiarity  shown  by  sunlight  when  thus  examined, 
namely,  that  the  coloured  band,  rainbowlike,  and  exhibit- 
ing a  regular  gradation  of  colour  from  red  at  the  one  end, 
through  orange,  yellow,  green,  and  blue,  to  violet  at  the 
other  end,  was  interspersed  by  very  numerous  thin  black 
lines.  The  nature  of  these  lines  was  discovered  by 
Kirchoff.  The  light  emitted  by  a  white-hot  body  shows 
a  continuous  spectrum ;  but  if  such  white  light  be  passed 
through  the  vapours  of  a  metal,  such  as  sodium,  a  portion 
is  absorbed.  For  example,  glowing  sodium  gas  shows  two 
yellow  lines,  very  close  together ;  but  if  this  light  is  passed 
through  the  vapour  of  sodium,  these  lines  are  extinguished 
if  the  correct  amount  of  vapour  be  interposed.  Now  it 
was  found  that  the  position  of  the  two  dark  lines  in  the 


182    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

sun's  spectrum,  discovered  by  Fraunhofer,  is  identical 
with  that  of  the  two  yellow  lines  visible  in  the  spectrum 
of  glowing  sodium  vapour  ;  and  Kirchoff  concluded  that 
this  coincidence  furnished  a  proof  of  the  presence  of 
sodium  in  the  sun.  Fraunhofer  had  named  these  lines 
D:  and  D2.  Similar  conclusions  were  drawn  from  obser- 
vations of  the  coincidence  of  other  black  solar  lines  with 
those  of  elements  found  on  the  earth  ;  and  the  presence 
of  iron,  lead,  copper,  and  a  host  of  elements  in  the  sun 
was  proved. 

In  1868  a  total  eclipse  of  the  sun  took  place;  an 
expedition  was  sent  to  India,  from  which  a  good  view  was 
to  be  obtained.  Monsieur  Janssen,  the  distinguished 
French  astronomer,  observed  a  yellow  line,  not  a  dark,  but 
a  bright  one,  in  the  light  which  reached  the  earth  from 
the  edge  or  '  limb  '  of  the  sun,  and  which  proceeded  from 
its  coloured  atmosphere  or  chromosphere.  It  was  for 
some  time  suspected  that  this  line,  which  was  almost 
identical  in  position  with  the  yellow  lines  of  sodium,  Dl 
and  D2,  and  which  Janssen  named  D3,  was  due  to 
hydrogen.  But  ordinary  hydrogen  had  never  been  found 
to  show  such  a  line  ;  and  after  Sir  Edward  Frankland  and 
Sir  Norman  Lockyer  had  convinced  themselves  by 
numerous  experiments  that  D3  had  nothing  to  do  with 
hydrogen,  they  ascribed  it  to  a  new  element,  the  exist- 
ence of  which  on  the  sun  they  regarded  as  probable  ; 
and  for  convenience,  they  named  this  undiscovered 
element  'helium/  from  the  Greek  word  for  the  sun, 


It  was  not  until  the  year  1895  that  helium  was  found 
on  the  earth.  After  the  discovery  of  argon  in  1894, 
Ramsay  repeated  some  experiments  which  had  previously 
been  made  by  Dr.  Hillebrand,  of  the  United  States  Geo- 
logical Survey.  Hillebrand  had  found  that  certain 
minerals,  especially  those  containing  the  somewhat  rare 


RADIUM  AND  ITS  PRODUCTS  183 

elements  uranium  and  thorium,  when  heated,  or  when 
treated  with  acids,  gave  off  a  gas  which  he  took  for 
nitrogen.  But  the  discovery  of  argon  had  taught  Ramsay 
how  to  deal  with  such  a  gas.  He  examined  it  in  the  hope 
that  it  might  lead  to  the  discovery  of  a  compound  of 
argon ;  but  its  spectrum  turned  out  to  be  identical  with 
that  of  solar  helium,  and  terrestrial  helium  was  discovered. 
It  proved  to  be  a  very  light  gas,  only  twice  as  heavy  as 
hydrogen,  the  lightest  substance  known ;  its  spectrum  con- 
sists chiefly  of  nine  very  brilliant  lines,  of  which  D3  is  the 
most  brilliant ;  it  has  never  been  condensed  to  the  liquid 
state,  and  is  the  only  gas  of  which  that  can  now  be  said 
(for  hydrogen  has  been  liquefied  within  the  last  few  years1), 
and,  like  argon,  it  has  not  been  induced  to  form  any 
chemical  compound.  That  it  is  an  element  is  shown  by 
the  relation  of  its  atomic  weight,  4,  to  that  of  other 
elements,  as  well  as  by  certain  of  its  properties,  the  most 
important  of  which  is  the  ratio  between  its  specific  heat 
at  constant  volume  and  constant  pressure ;  but  to  explain 
the  bearing  of  this  property  on  the  reasoning  which  proves 
it  to  be  an  element  would  be  foreign  to  the  subject  of  this 
article. 

This  then  was  the  elementary  substance  that  Ruther- 
ford and  Soddy  suspected  to  be  one  of  the  decomposition 
products  of  radium.  The  word  '  decomposition,'  however, 
implies  the  disruption  of  a  compound,  and  the  change 
which  takes  place  when  radium  produces  helium  is  of 
such  a  striking  nature  that  it  is  perhaps  preferable  to  use 
the  term  c  disintegration.' 

Having  procured  fifty  milligrammes  (about  three- 
quarters  of  a  grain)  of  radium  bromide,  Ramsay  and 
Soddy  placed  the  greyish-brown  crystalline  powder  in  a 
small  glass  bulb  about  an  inch  in  diameter.  This  bulb 
was  connected  by  means  of  a  capillary  tube  with  another 

1  It  has  since  been  liquefied  by  Kammerlingh  Onnes  of  Leiden. 


184    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 


bulb  of  about  the  same  size ;  on  each  side  of  the  second 
bulb  there  was  a  stop-cock,  as  shown  in  the  sketch.  To 
begin  with,  the  bulb  A  was  pumped  empty  of  air;  it 
contained  the  dry  bromide  of  radium.  The 
stop-cock  B  was  then  shut.  Next,  some 
water  was  placed  in  bulb  (7,  and  it  too  was 
pumped  free  from  air,  and  the  stop -cock  D 
was  closed.  B  was  then  opened,  so  that 
the  water  in  C  flowed  into  A ,  and  dissolved 
up  the  bromide  of  radium.  As  it  was 
dissolving,  gas  bubbles  were  evolved  with 
effervescence,  and  that  gas  collected  in  the 
two  bulbs,  A  and  B.  The  sketch  shows  the 
state  of  matters  after  the  water  had  been 
added  and  the  gas  evolved.  The  apparatus 
was  then  permanently  sealed  on  to  a  tube 
connected  with  a  mercury-pump,  so  con- 
trived that  gas  could  be  collected.  The  stop- 
cocks having  been  opened,  the  gas  passed 
into  the  pump,  and  was  received  in  a  small 
test-tube.  From  the  test-tube  it  was  passed  into  a  reservoir, 
where  it  was  mixed  with  pure  oxygen,  and  electric  sparks 
were  then  passed  through  it  for  some  hours,  a  little  caustic 
soda  being  present.  This  process  has  the  result  of  causing 
all  gases  except  those  like  argon  to  combine,  and  they  are 
therefore  removed.  It  was  easy  to  withdraw  oxygen  by 
heating  a  little  phosphorus  in  the  gas ;  and  it  was  then 
passed  into  a  small  narrow  glass  tube,  which  had  a  platinum 
wire  sealed  in  at  each  end — a  so-called  Plticker's  vacuum- 
tube.  On  passing  an  electric  discharge  from  a  Ruhmkorff 
induction-coil  through  the  gas  in  the  tube,  the  well-known 
spectrum  of  helium  was  seen. 

Thus  helium  was  proved  to  be  contained  in  radium 
bromide  which  had  stood  for  some  time.  The  specimen 
used  was  said  to  be  about  three  months  old,  and  the 


EXTRACTION  OP 

GASES  FROM 
RADIUM  BROMIDE 


RADIUM  AND  ITS  PRODUCTS  185 

helium  had  accumulated.    But  whence  came  the  helium  ? 
That  was  the  next  question  to  be  settled. 

A  solution  of  radium  bromide  gives  off  gas  continuously. 
That  gas,  on  investigation,  is  found  to  be  a  mixture  of 
oxygen  and  hydrogen,  the  constituents  of  the  water  in 
which  the  bromide  is  dissolved.  It  contains,  however,  a 
small  excess  of  hydrogen,  which  implies  that  some  oxygen 
has  been  absorbed,  probably  by  the  radium  bromide, 
although  what  becomes  of  that  excess  has  not  yet  been 
determined. 

When  an  electric  spark  is  passed  through  a  mixture  of 
oxygen  and  hydrogen,  an  explosion  takes  place;  the 
gases  combine,  and  water  is  formed.  Any  excess  of 
hydrogen  is,  however,  unaffected.  Now  the  gases  evolved 
from  a  solution  of  radium  bromide  make  glass  luminous  in 
the  dark,  and  possess  the  power  of  discharging  an  electro- 
scope, like  radium  bromide  itself.  Rutherford  and  Soddy 
discovered  that  when  this  mixture  of  gases  is  led  through 
a  tube  shaped  like  a  U,  cooled  to  -  185°  C.  by  dipping  in 
liquid  air,  the  luminous  gas  condenses,  and  the  gases 
which  pass  on  have  nearly  ceased  to  be  luminous  in 
the  dark,  and  no  longer  discharge  an  electroscope.  To 
such  condensable  gases  Rutherford  applied  the  term 
'  emanation ' ;  this  one  is  known  as  the  '  radium  emana- 
tion.' 

The  next  question  to  be  answered  was :  Is  the  helium 
evolved  from  the  radium  bromide  directly,  or  is  it  a  pro- 
duct of  the  emanation  ?  It  was  necessary,  therefore,  to 
collect  the  emanation  and  to  examine  its  spectrum.  This 
was  managed,  after  many  unsuccessful  trials,  by  exploding 
the  mixture  of  oxygen  and  hydrogen  containing  the 
emanation,  allowing  the  remaining  hydrogen  to  pass  into 
a  tube  containing  a  thin  spiral  of  slightly  oxidised  copper 
wire  kept  at  a  red  heat  by  an  electric  current:  the 
hydrogen  combined  with  the  oxygen  of  the  oxide  of 


186    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

copper,  and  formed  water.  The  apparatus  was  so  arranged 
that  mercury  could  be  allowed  to  enter  the  tube  from 
below,  so  as  to  sweep  before  it  any  remaining  gas ;  and 
the  water  was  removed  from  the  gas  by  making  it  pass 
through  a  tube  filled  with  a  suitable  absorbing  agent, 
followed  up  by  mercury.  The  gas  finally  entered  a  very 
small  spectrum-tube,  entirely  made  of  capillary  tubing, 
like  the  stem  of  a  thermometer.  On  passing  a  discharge 
from  a  coil  through  the  spectrum- tube  after  the  emanation 
had  been  thus  introduced,  a  spectrum  was  seen,  consisting 
of  some  bright  green  lines ;  but  it  was  extremely  difficult 
to  prevent  the  presence  of  traces  of  carbon  compounds, 
and  at  this  stage  their  spectrum  was  always  seen.  But 
the  D3  line  of  helium  was  absent.  After  a  couple  of  days, 
however,  a  faint  yellow  hue  began  to  appear,  identical  in 
position  with  D3 ;  and  as  time  went  on,  that  line  became 
more  distinct,  and  was  followed  by  the  other  lines  charac- 
teristic of  helium,  until,  after  a  week,  the  whole  helium 
spectrum  was  visible.  It  was  thus  proved  that  the  radium 
emanation  spontaneously  changes  into  helium.  Of  course 
other  substances  might  have  been,  and  undoubtedly  were, 
formed ;  but  these  it  was  not  possible  to  detect. 

The  next  problem  was  to  measure  the  amount  of 
emanation,  resulting  from  a  given  weight  of  radium,  in  a 
given  time.  The  method  of  procedure  was  similar  to  that 
already  described,  except  in  one  respect:  the  spiral  of 
oxidised  copper  wire  was  omitted,  and  the  excess  of 
hydrogen,  mixed  with  the  emanation,  was  cooled  in  a  small 
bulb  by  help  of  liquid  air.  This  condensed  the  emanation; 
and  the  hydrogen,  which  of  course  is  not  liquefied  at  the 
temperature  of  liquid  air,  was  pumped  away.  On  removal 
of  the  liquid  air,  the  emanation  became  gaseous,  and  it 
was  forced  by  means  of  mercury  into  a  minute  measuring 
tube,  like  the  very  narrow  stem  of  a  thermometer.  It 
was  thus  possible  to  measure  its  volume.  It  is  a  well- 


RADIUM  AND  ITS  PRODUCTS  187 

known  law  that  gases  decrease  in  volume  proportionally 
to  increase  of  pressure ;  if  the  pressure  is  doubled,  the 
volume  of  the  gas  is  halved,  and  so  on.  Now  this  was  found 
to  be  the  case  with  the  emanation ;  hence  the  conclusion 
that  it  is  a  gas,  in  the  ordinary  meaning  of  the  word. 
But  it  is  a  very  unusual  gas ;  for  not  only  is  it  luminous 
in  the  dark,  but  it  slowly  contracts,  day  by  day,  until  it 
practically  all  disappears.  It  does  not  lose  its  luminosity, 
however;  what  remains,  day  by  day,  is  as  luminous  as 
ever ;  but  its  volume  decreased,  until  after  about  twenty- 
five  days  the  gas  had  contracted  to  a  mere  luminous 
point.  What  had  become  of  the  helium  ?  That  was  dis- 
covered on  heating  the  tube.  It  is  well  known  that  glass, 
exposed  to  the  radium  emanation,  turns  purple,  if  it  is 
soda  glass;  brown,  if  it  is  potash  glass.  This  is  due  to 
the  penetration  of  the  glass  by  the  electrons,  which  are 
exceedingly  minute  particles,  moving  with  enormous 
velocity.  When  the  emanation  changes  into  helium, 
the  molecules  of  that  gas  are  also  shot  off  with  enormous 
velocity,  although  they  move  much  more  slowly  than  the 
electrons.  It  is  sufficient,  however,  to  cause  them  to 
penetrate  the  glass ;  but  on  heating  they  are  evolved,  and 
collect  in  the  tube,  and  the  volume  of  the  helium  can  be 
measured.  It  turned  out  to  be  three  and  a  half  times 
that  of  the  emanation.  But  as  the  emanation  is  probably 
fifty  times  as  heavy  as  hydrogen,  all  the  emanation  is 
not  accounted  for  by  the  volume  of  helium  found;  it  is 
almost  certain  that  solid  products  are  formed,  which  are 
deposited  on  the  glass,  and  which  are  radioactive.  Up  to 
the  present  these  products  have  not  been  investigated 
chemically. 

It  was  possible,  knowing  the  volume  of  the  emanation, 
and  knowing  also  the  volume  which  the  radium  would 
have  occupied  had  it,  too,  been  gaseous  (for  a  simple  rule 
enables  chemists  to  know  the  volume  which  a  given 


188    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

weight  of  any  element  would  occupy  in  the  state  of  gas), 
to  calculate  how  long  it  would  take  for  the  radium  to  be 
converted  into  emanation,  supposing  that  to  be  its  only 
product.  This  gives  for  half  of  the  radium  to  be  decom- 
posed about  1150  years.  But  there  is  a  good  deal  of 
conjecture  about  the  calculation;  for  many  unproved 
assumptions  have  to  be  made. 

A  further  experiment,  conducted  in  a  somewhat  similar 
manner,  but  with  the  utmost  precaution  to  exclude  every 
trace  of  foreign  gas,  made  it  possible  to  measure  the 
position  of  the  lines  of  the  spectrum  of  the  emanation. 
In  general  it  may  be  said  that  the  spectrum  has  a  similar 
character  to  those  of  argon  and  helium ;  it  consists  of  a 
number  of  bright  lines,  chiefly  green,  appearing  distinctly 
on  a  black  background.  It  confirms  the  supposition, 
made  after  examination  of  the  chemical  properties  of  the 
emanation,  that  it  is  a  gas  belonging  to  the  argon  group, 
with  a  very  heavy  atomic  weight.  Some  of  the  lines  of 
the  spectrum  appear  to  be  identical  with  lines  observed  in 
the  spectra  of  the  stars ;  and  it  may  perhaps  be  inferred 
that  such  heavenly  bodies  are  rich  in  radium. 

In  the  diagram  on  page  184,  the  bulb  containing  radium 
bromide  there  shown  was  surrounded  by  a  small  glass 
beaker,  as  a  precautionary  measure.  As  a  matter  of 
fact,  there  were  three  such  bulbs  and  three  such  beakers, 
on  the  principle  of  not  putting  all  one's  eggs  in 
one  basket.  These  beakers  had  never  been  in  contact 
with  the  radium  bromide,  nor  with  the  emanation ;  but 
they  had  been  bombarded  for  months  by  /3-rays,  or 
electrons,  which  are  so  minute,  and  move  so  rapidly,  that 
they  penetrate  thin  glass  with  ease.  It  was  found  that 
these  beakers  were  radioactive ;  and  it  is  very  remarkable 
that  after  washing  with  water,  the  beakers  lost  their  radio- 
activity, which  was  transferred  to  the  water.  Evidently, 
then,  some  radioactive  matter  had  been  produced  by  the 


RADIUM  AND  ITS  PRODUCTS  189 

influence  of  the  /3-rays.  On  investigation,  it  was  proved 
that  more  than  one  substance  had  been  produced.  For 
on  bubbling  air  through  the  water,  a  radioactive  gas 
passed  away  along  with  the  air ;  it  had  the  power  of  dis- 
charging an  electroscope,  but  its  life  lasted  only  a  few 
seconds.  It  was  only  while  the  current  of  air  was  passing 
through  the  electroscope  that  the  gold-leaves  fell  together; 
on  ceasing  the  current,  the  leaves  remained  practically 
stationary.  Now  had  radium  emanation  been  introduced 
into  the  electroscope,  its  effect  would  have  lasted  twenty- 
eight  days ;  had  the  emanation  from  thorium  been  intro- 
duced, it  would  have  taken  about  a  minute  before  it  ceased 
to  cause  the  gold-leaves  to  fall  in.  There  is  an  emanation, 
however,  that  from  actinium,  which  is  very  short-lived, 
and  it  looks  probable  that  one  of  the  substances  produced 
from  the  /3-rays  is  actinium.  But  it  is  not  the  only  one. 
For  the  water  with  which  the  glass  was  washed  gives  a 
radioactive  residue  after  evaporation  to  dryness;  and  it 
contains  a  substance  which  forms  an  insoluble  chloride, 
sulphide,  and  sulphate,  though  the  hydroxide  is  soluble  in 
ammonia.  Either,  then,  the  /S-rays  have  so  altered  the 
constituents  of  the  glass  that  new  radioactive  elements  are 
formed  ;  or  perhaps  it  is  the  air  which  surrounds  the  glass 
which  has  yielded  these  new  elements;  or  it  may  be, 
though  this  appears  less  probable,  that  the  /3-rays  them- 
selves, which  are  identical  with  electrons,  or  '  atoms '  of 
negative  electricity,  have  condensed  to  form  matter. 

Such  are  some  of  the  results  which  have  been  obtained 
in  a  chemical  examination  of  the  products  of  change  of 
radium.  The  work  is  merely  begun,  but  it  leads  to  a 
hypothesis  as  regards  the  constitution  of  radium  and 
similar  elements,  which  was  first  put  forward  by  Ruther- 
ford and  Soddy.  It  is  that  atoms  of  elements  of  high 
atomic  weight,  such  as  radium,  uranium,  thorium,  and  the 
suspected  elements  polonium  and  actinium,  are  unstable ; 


190    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

that  they  undergo  spontaneous  change  into  other  forms  of 
matter,  themselves  radioactive,  and  themselves  unstable ; 
and  that  finally  elements  are  produced  which,  on  account 
of  their  non-radioactivity,  are,  as  a  rule,  impossible  to 
recognise,  for  their  minute  amount  precludes  the  applica- 
tion of  any  ordinary  test  with  success.  The  recognition  of 
helium,  however,  which  is  comparatively  easy  of  detection, 
lends  great  support  to  this  hypothesis. 

The  natural  question  which  suggests  itself  is :  Are  other 
elements  undergoing  similar  change?  Can  it  be  that 
their  rate  of  change  is  so  slow  that  it  cannot  be  detected  ? 
Professor  J.  J.  Thomson  has  attempted  to  answer  this 
question,  and  he  has  found  that  many  ordinary  elements 
are  faintly  radioactive ;  but  the  answer  is  still  incomplete, 
for,  first,  radium  is  so  enormously  radioactive  that  the 
merest  trace  of  one  of  its  salts  in  the  salt  of  another 
element  would  produce  such  radioactivity ;  and,  second,  it 
is  not  proved  that  radioactivity  is  an  invariable  accompani- 
ment of  such  change ;  or,  again,  it  may  be  evolved  so 
slowly  as  to  escape  detection.  A  lump  of  coal,  for 
example,  is  slowly  being  oxidised  by  the  oxygen  of  the 
air;  oxidation  is  attended  by  a  rise  of  temperature,  but 
the  most  delicate  thermometer  would  detect  no  difference 
between  the  temperature  of  a  lump  of  coal  and  that 
of  the  surrounding  air,  for  the  rate  of  oxidation  is  so 
slow. 

Another  question  which  arises  is :  Seeing  that  an  element 
like  radium  is  changing  into  other  substances,  and  that  its 
life  is  a  comparatively  short  one,  it  must  be  in  course  of 
formation,  else  its  amount  would  be  exhausted  in  several 
thousand  years.  An  attempt  has  been  made  by  Soddy  to 
see  if  uranium  salts,  carefully  purified  from  radium,  have 
reproduced  radium  after  an  interval  of  a  year;  but  his 
result  was  a  negative  one.  Possibly  some  other  form  of 
matter  besides  uranium  contributes  to  the  synthesis  of 


RADIUM  AND  ITS  PRODUCTS  191 

radium,  and  further  experiments  in  this  direction  will  be 
eagerly  welcomed.1 

Lastly,  the  experiments  of  Ramsay  and  Cook,  of 
which  an  account  has  been  given,  on  the  action  of  the 
/3-rays  appear  to  foreshadow  results  of  importance. 
For  while  radium,  during  its  spontaneous  change,  parts 
with  a  relatively  enormous  amount  of  energy,  largely 
in  the  form  of  heat,  it  is  a  legitimate  inference  that 
if  the  atoms  of  ordinary  elements  could  be  made  to 
absorb  energy,  they  would  undergo  change  of  a  con- 
structive and  not  of  a  disruptive,  nature.  If,  as  looks 
probable,  the  action  of  /3-rays,  themselves  the  con- 
veyers of  enormous  energy,  on  such  matter  as  glass, 
is  to  build  up  atoms  which  are  radioactive,  and  con- 
sequently of  high  atomic  weight ;  and  if  it  be  found  that 
the  particular  matter  produced  depends  on  the  element 
on  which  the  /3-rays  fall,  and  to  which  they  impart  their 
energy : — if  these  hypotheses  are  just,  then  the  transmuta- 
tion of  elements  no  longer  appears  an  idle  dream.  The 
philosopher's  stone  will  have  been  discovered,  and  it  is 
not  beyond  the  bounds  of  possibility  that  it  may  lead  to 
that  other  goal  of  the  philosophers  of  the  dark  ages — the 
elixir  vitce.  For  the  action  of  living  cells  is  also  dependent 
on  the  nature  and  direction  of  the  energy  which  they 
contain;  and  who  can  say  that  it  will  be  impossible  to 
control  their  action,  when  the  means  of  imparting  and 
controlling  energy  shall  have  been  investigated  ? 

1  There  appears  to  be  an  intermediate  product  to  which  the  name 
'  ionium  '  has  been  given  by  Boltwood,  its  discoverer. 


WHAT  IS  ELECTRICITY  ? 

AN  old  friend  of  mine,  by  profession  a  banker,  who 
spent  a  large  portion  of  his  life  of  eighty-nine  years  in 
studying  geology  and  astronomy,  once  put  to  me  the 
question :  '  Whence  comes  the  motive  power  of  electricity  ? 
I  can  understand  the  motive  power  of  steam,  but  not  of 
electricity.5 

This  led  me  to  think  on  the  subject ;  and  although  there 
is  not  much  new  in  my  reply,  it  contains,  nevertheless,  one 
novel  point,  which  contributes,  I  think,  to  clearness  of 
thought. 

The  answer  refers  only  to  electricity  generated  by  a 
battery;  not  to  a  current  made  by  means  of  a  dynamo 
machine.  The  answer  to  the  question,  What  generates  a 
current  in  a  dynamo  ?  must  be  left  till  a  later  oppor- 
tunity. 

The  simplest  form  of  a  battery  consists  of  a  vessel 
containing  dilute  hydrochloric  acid,  into  which  dip  a 
copper  and  zinc  plate,  connected  by  a  wire.  A  current 
flows  through  the  wire ;  its  presence  can  be  demonstrated 
by  a  galvanometer,  or  by  dipping  the  wire  from  the  copper 
plate  and  the  wire  from  the  zinc  plate  into  a  solution  of 
iodide  of  potassium;  a  brown  stain  begins  to  appear  at 
the  end  of  the  wire  connected  with  the  zinc  plate ;  it  is 
caused  by  the  iodine  being  set  free,  which  dissolves  in  the 
liquid  with  a  brown  colour. 

If  it  is  desired  to  make  the  test  more  striking  a  little 
starch  may  be  added  to  the  solution  of  iodide  of  potassium. 


194    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

The  colour  will  then  be  blue,  for  iodine  and  starch  give  a 
blue  colour.    Now  why  does  the  current  pass  ? 

To  explain  this,  let  us  consider  what  happens  to  a 
lump  of  sugar  lying  at  the  bottom  of  a  cup  of  water. 
After  a  few  minutes  the  sugar  will  melt,  or,  more  cor- 
rectly, dissolve  in  the  water.  But  the  water  at  the  top 
will  not  be  sweet  for  a  long  time ;  the  sugar  takes  a  good 
many  minutes  before  it  spreads  up  into  the  water.  Why  ? 
It  is  believed  that  sugar  consists  of  minute  invisible 
particles  called  molecules ;  and  they  are  in  motion. 

Although  we  cannot  see  molecules  move,  we  may 
nevertheless  make  an  experiment  which  will  prove  to  us 
that  particles  of  matter,  easily  visible  under  a  fairly 
powerful  microscope,  are  always  in  rapid  motion. 

An  ordinary  water-colour  paint,  rubbed  with  water, 
gives  particles  of  a  convenient  size ;  gamboge  is  perhaps 
the  best  colour  to  take.  These  particles  are  always 
' jigging'  to  and  fro;  their  motion  is  not  regular,  but 
spasmodic;  and  they  spread,  in  virtue  of  that  motion; 
so  that  they  move  from  one  part  of  the  water  to 
another. 

So  it  is  with  the  sugar  molecules ;  that  they  do  spread 
is  proved  by  the  water  becoming  sweet,  even  at  the 
surface.  In  fact  the  sugar  particles  try  to  move  from 
where  they  are  to  where  they  are  not.  If  one  felt  inclined 
to  moralise  on  the  subject,  one  might  ask,  Is  not  that 
what  we  all  try  to  do  ?  Is  not  an  attempt  at  motion  what 
makes  for  progress  of  all  kinds  in  the  world  ? 

If  such  motion  could  be  hindered,  say  by  a  screen  which 
would  block  the  passage  of  the  sugar  molecules,  while 
allowing  the  water  molecules  to  pass,  the  sugar  molecules 
would  bombard  the  screen,  giving  it  innumerable  blows, 
and  these  blows  would  make  themselves  evident  as  a  kind 
of  pressure  on  the  screen. 

This  pressure  has  been  measured ;  a  partition  has  been 


WHAT  IS  ELECTRICITY?  195 

found  which  allows  the  water  to  pass,  while  blocking  the 
way  for  sugar.  It  is  as  if  gravel  of  two  sizes  were  being 
shaken  on  a  sieve;  the  stones  which  pass  through  the 
meshes  do  not  press  on  the  sieve,  while  those  which  are 
stopped  by  the  sieve  may  be  recognised  by  their 
pressure. 

Substances  other  than  sugar,  too,  can  be  stopped  by  the 
same  screen ;  for  example,  tartaric  acid  can.  And  it  has 
been  found  that  the  pressure  produced  by  equal  numbers 
of  molecules  or  particles  of  sugar  and  of  tartaric  acid, 
contained  in  equal  volumes  of  water,  is  equal. 

Common  salt  is  a  compound  of  a  metal  named  sodium 
and  a  yellow-green  gas  called  chlorine.  Each  molecule  or 
particle  of  salt  must  therefore  contain  these  two  elements ; 
that  is,  each  particle  must  be  made  up  of  at  least  two 
smaller  particles,  and  these  smaller  particles  are  called 
'  atoms/  If  a  spoonful  of  salt  be  placed  at  the  bottom  of 
a  glass  of  water,  like  the  sugar,  its  particles  will  wander 
through  the  water,  so  that,  after  some  time,  the  water  will 
become  salt  all  through. 

Just  as  with  sugar,  it  is  possible  to  find  a  membrane 
which  will  allow  water  to  pass  through  it,  while  it  stops 
the  passage  of  salt;  and  it  is  possible  to  measure  the 
pressure  of  molecules  of  salt  on  the  membrane. 

Now  here  a  very  curious  thing  has  been  found ;  mole- 
cules of  salt  give  twice  as  great  a  pressure  as  an  equal 
number  of  particles  of  sugar,  spread  through  the  same 
volume  of  water ;  it  looks  as  if  there  were  twice  as  many 
particles  of  salt  present.  And  it  is  supposed  that  there 
really  are  twice  as  many.  To  account  for  this,  it  is 
believed  that  each  molecule  of  salt  splits  up  into  two 
atoms,  one  of  sodium  and  one  of  chlorine,  and  that  each 
atom  plays  the  part  of  a  molecule,  in  so  far  as  it  is  able  to 
raise  pressure.  Owing  to  the  habit  which  such  minute 
particles  as  the  atoms  of  sodium  and  chlorine  have  of 


196    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

moving  about  in  a  watery  solution,  they  are  named  '  ions,' 
a  Greek  word,  which  means  '  wanderers.' 

But  an  ion  is  not  merely  a  wandering  particle;  the 
moving  particles  of  sugar  are  not  called  ions.  The  ions 
contained  in  a  solution  of  salt  have  another  peculiarity ; 
one  has  gained,  and  the  other  has  lost,  what  we  may  term 
an  atom  of  electricity.  Now  what  is  electricity  ? 

It  used  to  be  believed,  formerly,  that  there  were  two 
kinds  of  electricity,  one  called  positive  and  the  other 
negative.  At  that  time  it  would  not  have  been  possible 
to  answer  the  question.  But  recent  researches  make  it 
probable  that  what  used  to  be  called  negative  electricity 
is  really  a  substance.  Indeed  the  relative  weight  of  its 
particles  has  been  measured;  each  is  about  one  seven- 
hundredth  of  the  mass  of  an  atom  of  hydrogen  :  and  the 
mass  of  an  atom  of  hydrogen  is  the  smallest  of  all 
masses  of  what  we  have  been  used  to  call  matter. 

Atoms  of  electricity  are  named  '  electrons ' ;  they  appear 
to  be  all  of  one  kind.  The  metal  sodium,  and  indeed  all 
other  metals,  may  be  regarded  as  compound  of  electrons 
with  a  stuff  which  may  be  named  '  sodion '  for  sodium, 
'  cuprion '  for  copper, '  ferrion '  for  iron,  and  so  on.  When 
sodium  loses  an  electron  it  becomes  '  sodion ' ;  when  iron 
loses  three  electrons  it  becomes  '  ferrion,'  and  similarly 
with  the  rest. 

How  can  sodium  be  made  to  lose  its  electron  ?  This 
happens  when  it  enters  into  combination.  When  sodium 
is  heated  in  air,  which  contains  oxygen  gas,  it  burns,  and 
is  said  to  unite  or  combine  with  oxygen  ;  burning  appears 
to  be  accompanied  by  a  transference  of  an  electron  from 
the  sodium  to  the  oxygen.  Common  salt  may  be  made 
by  heating  sodium  in  chlorine  gas ;  it  takes  fire,  burns 
and  is  changed  into  white  ordinary  salt.  It  has  lost  an 
electron ;  chlorine  has  gained  one. 

When  dissolved  in  water,  the  sodium  exists  in  the  water 


WHAT  IS  ELECTRICITY  ?  197 

as  sodion ;  that  is,  sodium  less  an  electron.  The  chlorine 
is  in  the  water,  not  as  chlorine ;  by  gaining  an  electron,  it 
has  been  converted  into  chlorion.  We  see,  therefore,  that 
those  elements  which  we  call  metals  become  ions  by 
losing  electrons;  while  those  which  we  call  non-metals 
become  ions  by  gaining  electrons. 

Let  us  now  consider  the  simple  battery  or  cell,  consist- 
ing of  a  plate  of  copper  and  a  plate  of  zinc,  dipping  in  a 
jar  half  full  of  dilute  hydrochloric  acid.  This  hydro- 
chloric acid  consists  of  a  number  of  ions  of  hydrogen; 
and  ions  of  hydrogen  differ  from  ordinary  hydrogen  gas 
in  the  same  way  as  ions  of  sodium  differ  from  metallic 
sodium,  namely,  by  each  atom  having  parted  with  an 
electron.  The  electron  which  each  atom  has  lost  has 
attached  itself  to  an  atom  of  chlorine,  and  the  chlorine 
atom  is  thereby  converted  into  an  ion. 

The  plate  of  zinc  cannot  dissolve  in  the  water,  until  its 
atoms  have  been  converted  into  ions.  They  would  then 
each  have  to  part  with  two  electrons.  But  the  attraction 
of  an  atom  of  zinc  for  these  two  electrons  is  so  great  that 
the  zinc  does  not  dissolve,  unless,  indeed,  the  electrons 
can  be  conveyed  elsewhere. 

Now  electrons  have  the  power  of  travelling  through 
metal;  this  point  will  be  considered  later;  it  must  be 
accepted  for  the  present.  When  an  atom  of  zinc  gives  up 
its  two  electrons  to  the  zinc  plate,  the  atom  of  zinc  which 
lies  nearest  to  that  which  has  parted  with  these  two  elec- 
trons will  be  overloaded ;  it  already  is  in  combination  with 
its  own  two,  and  cannot  unite  with  two  additional  ones ; 
or,  if  it  does,  it  must  pass  on  its  own  electrons  to  the 
neighbouring  atom. 

These  two  electrons,  therefore,  displace  others,  or,  it  may 
be,  are  themselves  transmitted  through  the  zinc,  until 
they  reach  the  copper  wire.  Copper,  in  the  metallic 
state,  is  also  a  compound  of  copper  ions  with  two  elec- 


198    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

trons ;  and  the  copper,  like  the  zinc,  is  overloaded  by  the 
electrons  from  the  zinc.  Hence  it  transmits  them  to  the 
copper  plate,  and  they  find  their  way  to  the  surface  of  the 
plate. 

There  they  find  hydrogen  ions,  which  are  ready  to  com- 
bine each  with  one  electron  in  order  to  form  hydrogen 
atoms ;  and  having  combined,  the  atoms  of  hydrogen 
unite  in  couples,  bubbles  of  hydrogen  are  formed,  and 
float  up  to  the  surface  and  burst.  In  short,  the  zinc 
passes  on  its  electrons  through  the  copper  wire  to  the 
copper  plate,  when  they  are  transmitted  to  the  ions  of 
hydrogen  in  solution,  and  these  first  become  atoms  and 
then  molecules. 

These  conceptions,  which  are  rather  intricate,  may  be 
rendered  clearer  by  means  of  a  diagram,  a  is  the  solu- 
tion of  hydrochloric  acid  in  water ;  b  is  the  zinc  plate ; 
c  is  the  copper  plate,  and  d  the  connecting  wire.  H  H,  on 
the  left  of  the  diagram,  are  two  atoms  of  hydrogen,  each 


c  b 

EXPLANATION   OF  A  GALVANIC   CELL 

of  which  has  gained  an  electron ;  they  will  unite  together 
to  a  molecule,  and  escape  in  a  bubble  up  through  the 


WHAT  IS  ELECTRICITY?  199 

liquid.  The  electrons  which  they  have  gained  have 
followed  the  arrows  from  the  zinc  plate,  along  the  copper 
wire  and  down  the  copper  plate. 

A  zinc  atom  minus  its  two  electrons  has  left  the  zinc 
plate ;  it  is  now  a  zinc  ion.  These  two  electrons  have  dis- 
placed other  electrons  from  their  combination  with  zinc 
and  copper ;  and  it  is  these  electrons,  or  their  substitutes, 
which  have  attached  themselves  to  the  hydrogen  ions. 
There  are  hydrogen  and  chlorine  ions  in  the  liquid.  The 
hydrogen  ions  move  toward  the  copper  plate,  and  the 
chlorine  ions  toward  the  zinc  plate,  but  less  rapidly. 

Some  of  these  will  touch  the  zinc  plate ;  and  if  they 
could  pass  round  the  circuit,  through  the  wire,  there 
would  be  no  electric  pressure ;  but  it  is  because  the  plates 
and  the  connecting  wire  are  impervious  to  matter,  while 
they  are  pervious  to  electrons,  that  electric  pressure — or 
to  give  it  the  usual  name,  electromotive  force  or  potential 
— is  developed.  In  fact,  the  metals  and  the  wire  are  semi- 
permeable  membranes ;  they  allow  electrons  to  pass,  while 
they  block  the  passage  of  matter. 

Perhaps  the  idea  may  be  somewhat  more  easily  grasped 
if  it  is  put  in  another  form.  Electrons  do  not  pass 
through  water ;  probably  because  the  treble  combination 
of  electrons,  hydrogen,  and  oxygen  is  too  firm  to  allow 
of  the  transference  of  electrons  from  one  molecule  to 
another.  But  when  a  salt  is  dissolved  in  the  water  elec- 
trons can  pass,  for  they  easily  transfer  themselves  from  one 
place  to  another,  carrying  along  with  them  atoms  such  as 
chlorine.  Their  progress  is  much  impeded  thereby ;  but, 
as  explained  before,  they  are  easily  transmitted  through 
metals,  and  thus,  again,  electric  pressure  is  developed. 

The  analogy  with  '  osmotic  pressure,'  as  the  pressure  of 
the  sugar  molecules  dissolved  in  water  against  a  semi- 
permeable  membrane  is  called,  is  obvious;  just  as  the 
water  in  which  the  sugar  is  dissolved  can  pass  in  and  out 


200    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

through  the  semi-permeable  screen  or  partition,  so  the 
electrons  can  pass  backwards  and  forwards  through  the 
metallic  plates  and  wire;  and  just  as  the  sugar  molecules 
are  unable  to  traverse  the  membrane,  so  the  matter  with 
which  the  electrons  are  in  combination  is  unable  to  pass 
through  the  metal.  The  metal  is  thus  a  semi-permeable 
membrane,  and  electric  pressure  is  developed  in  con- 
sequence, in  the  same  way  as  osmotic  pressure  is  developed 
by  the  sugar  in  solution. 

If  a 'weak  solution  of  common  salt  be  boiled  down,  after 
sufficient  water  has  been  evaporated  away,  crystals  of  salt 
separate  out  and  deposit.  Now  the  weak  solution  con- 
tains the  constituents  of  the  salt  almost  entirely  in  the 
state  of  ions ;  that  is,  the  sodion  is  without  an  electron, 
which,  if  added,  would  convert  it  into  the  metal  sodium ; 
and  the  chlorion  would  be  the  element  chlorine,  if  it 
could  part  with  its  electron. 

During  concentration,  as  the  water  evaporates,  the  ions 
of  sodium  and  chlorine  are  brought  nearer  each  other, 
and  they  combine  to  form  solid  salt  when  enough  water 
has  been  removed.  But  even  when  combined  to  form 
salt  in  the  solid  state,  the  electron  does  not  leave  the 
chlorion  and  attach  itself  to  the  sodion ;  if  that  happened 
the  result  would  be  metallic  sodium  and  chlorine  gas; 
and  they  are  certainly  not  formed.  A  crystal  of  salt 
differs  from  a  solution  of  salt  in  much  the  same  respects 
as  a  piece  of  ice  differs  from  water ;  the  one  is  solid  and 
the  other  is  liquid ;  but  evidently  the  same  stuff  is  there ; 
the  only  difference  is  in  the  solidification. 

It  must  therefore  be  supposed  as  a  legitimate  inference 
that  when  a  lump  of  sodium  unites  with  chlorine  and 
burns  in  it  as  a  lump  of  coal  burns  in  air,  the  act  of 
combination  consists  of  the  transference  of  an  electron 
from  the  sodium  metal  to  the  chlorine ;  the  result  of  this 
transference  is  to  convert  the  sodium  metal  into  sodions 


WHAT  IS  ELECTRICITY?  201 

and  the  chlorine  gas  into  chlorions.  These  are  substances 
with  quite  different  physical  and  chemical  properties  from 
the  metal  sodium  and  the  gas  chlorine. 

On  dissolving  in  a  little  water,  some  of  the  chlorions 
and  sodions,  but  only  a  few,  become  separated ;  however, 
if  water  be  added  so  as  to  dilute  the  solution,  a  larger  and 
larger  number  separate,  until  at  a  sufficient  dilution  all 
are  separated.  In  fact,  if  this  conception  be  extended, 
all  chemical  combinations  should  be  regarded  as  the 
transference  of  electrons  from  one  set  of  elements  to 
another. 

But  not  all  compounds  are  split  into  ions  when  they 
are  dissolved;  it  may  be  conjectured  that  in  the  case  for 
instance  of  such  a  compound  as  sugar,  which  dissolves  in 
water  as  such,  the  atoms  of  carbon,  hydrogen,  and  oxygen, 
of  which  it  consists,  have  interchanged  electrons,  otherwise 
chemical  combination  would  not  exist ;  but  that  the  ions 
do  not  part  from  each  other,  even  when  opportunity  is 
given  by  dissolving  the  sugar  in  water. 

Although  facilities  for  motion  in  many  cases  lead  to 
separation  of  ions,  it  does  not  follow  that  when  facilities 
are  present  separation  will  always  take  place. 

When  common  salt  is  melted,  which  takes  place  if  it  be 
heated  to  redness,  the  ions  separate ;  that  this  is  the  case 
is  proved  by  its  being  then  able  to  conduct  electricity. 
Melted  glass  is  also  a  conductor,  although  solid  glass  is 
not ;  and  the  reason  again  is  probably  in  the  fact  that  the 
ions  have  no  freedom  of  motion  in  the  solid. 

These  considerations,  however,  though  closely  connected 
with  the  nature  of  ions,  are  not  in  such  close  touch  with 
the  subject  of  this  essay,  the  motive  power  of  electricity. 
Perhaps  a  last  analogy  may  make  the  explanation  which 
I  have  tried  to  give  somewhat  clearer ;  it  is  this : 

Place  a  dilute  solution  of  salt  in  one  vessel  and  a 
concentrated  solution  in  another ;  cover  both  vessels  with 


202    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

a  bell  jar;  pump  out  all  air,  so  that  the  bell  jar  is  filled 
only  with  vapour  of  water,  and  leave  the  whole  standing 
for  a  long  time.  The  weak  solution  will  grow  stronger, 
for  it  will  evaporate;  and  the  strong  solution  will  grow 
weaker,  for  the  vapour  of  water  will  condense  in  it.  Now 
imagine  that  the  two  salt  solutions  are  placed,  not  under 
the  same  bell  jar,  but  under  two  separate  bell  jars,  and 
that  these  bell  jars  are  connected  by  a  pipe.  In  the 
middle  of  this  pipe  is  a  little  engine ;  the  pipe  from  the 
weak  solution  enters  the  steam  pipe  of  the  cylinder,  and 
the  pipe  leading  from  the  cylinder,  which  would  in  an 
ordinary  engine  lead  to  the  exhaust,  is  connected  with  the 
bell  jar  containing  the  stronger  salt  solution;  then,  if  the 
engine  is  delicate  enough,  it  will  be  driven  by  the  current 
of  vapour  passing  from  the  weak  salt  solution  to  the  strong 
one. 

Why?  Because  although  steam  can  pass  away  from 
the  surface  of  the  water,  salt  cannot ;  the  surface  of  the 
water  is  a  diaphragm  which  will  allow  steam  to  pass,  but 
which  is  impenetrable  for  salt. 

The  analogy  with  a  battery  is  this:  The  zinc  plate  is 
like  the  weak  solution  of  salt ;  when  it  dissolves,  it  gives 
up  electrons  at  its  surface ;  these  electrons  can  pass  along 
the  wire,  which  is  the  analogue  of  the  steam-pipe;  if 
required,  a  small  magneto-electric  engine  could  be  inter- 
posed so  that  it  would  be  driven  by  the  current  passing 
through  the  wire,  that  is,  by  the  stream  of  electrons, 
just  as  the  steam-engine  is  driven  by  the  current  of 
steam. 

On  arriving  at  the  copper  plate  the  electrons  combine 
with  hydrogen  ions  and  escape ;  and  in  this  respect  the 
battery  described  resembles  rather  a  high  pressure  engine. 
But  if  desired  the  electrons  may  be  kept  in  the  system ;  it 
is  only  necessary  to  surround  the  copper  plate  with  some 
substance  such  as  sulphate  of  copper,  and  the  electrons 


WHAT  IS  ELECTRICITY  ?  203 

are  retained  by  uniting  with  the  copper  ions,  when  copper 
atoms  will  be  deposited  on  the  copper  plate. 

Just  as  the  surface  of  the  water  forms  a  diaphragm 
through  which  salt  cannot  pass,  while  steam  can,  so  the 
surface  of  the  zinc  plate  forms  a  diaphragm  through 
which  matter  such  as  zinc,  hydrogen,  or  chlorine  ions 
cannot  pass,  while  electrons  can,  and  they  are  also  able  to 
be  conveyed  by  the  wire,  as  steam  is  conveyed  through 
the  pipe.  The  motive  power  both  of  steam  and  electricity, 
in  a  word,  is  due  to  their  passing  from  a  region  where 
their  pressure  is  high  to  where  it  is  low. 


THE  AURORA  BOREALIS 

THE  Northern  Lights,  or  the  Merry  Dancers,  as  they  are 
often  called,  must  have  attracted  attention  in  our  country 
ever  since  it  was  inhabited.  But  whether  owing  to  their 
frequent  appearance  they  escaped  chronicling,  or  whether 
records  of  natural  phenomena  were  regarded  as  unim- 
portant, I  can  find  no  mention  of  them  in  Scottish  records. 
South  of  the  border  and  across  the  English  Channel 
mention  is  occasionally  made  of  them ;  for  in  these  more 
southern  regions  their  occurrence  was  sufficiently  un- 
common for  the  display  to  attract  attention.  They  were 
often  supposed  to  portend  disaster.  An  account  of  an  aurora 
seen  in  London  in  1560  likens  it  to  '  burning  spears ' : — 

1  Fierce  fiery  warriors  fight  upon  the  clouds, 
In  ranks  and  squadrons  and  right  form  of  war.' 

An  aurora  was  described  by  Cornelius  Genune,  Professor 
at  Lou  vain,  in  1575 ;  several  were  seen  by  Michael  Mestlin, 
tutor  to  the  famous  Kepler,  in  1580;  and  in  April  and 
September  1581,  and  in  September  1621,  brilliant  auroras 
were  chronicled.  From  that  date  until  1707  there  is  no 
mention  of  an  aurora  having  been  seen. 

It  has  long  been  known  that  the  compass-needle,  which 
usually  points  northward,  and  is  inclined  at  an  angle  to 
the  horizon  (or  is  said  to  '  dip '),  becomes  disturbed  and 
oscillates  when  an  aurora  is  seen  in  the  sky.  It  was  the 
celebrated  Halley1  who,  in  1714,  hazarded  the  bold  con- 
jecture that  the  aurora  was  therefore  a  magnetic  pheno- 

1  Philosophical  Transactions,  xxix.  No.  341. 

205 


206    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

menon ;  the  oscillations  of  the  compass  may  even  exceed 
ten  minutes  of  arc,  as  observed  by  Mr.  James  Glaisher l  in 
1847.  And  many  hypotheses  have  been  brought  forward 
to  account  for  the  connection  between  the  two  simul- 
taneous phenomena.  The  last  few  years  have  seen  the 
equipment  of  expeditions  to  Iceland,  Finland,  and  Northern 
America,  which  have  had  for  their  principal  object  the 
observation  of  the  earth's  magnetic  disturbances  and  the 
corresponding  auroral  displays.  Many  theories  have  been 
advanced,  and  it  will  be  my  task  to  try  to  bring  them 
before  you,  and  to  supplement  them  where  they  appear  to 
be  wanting. 

Let  us  first,  however,  listen  to  an  eloquent  description 
of  the  Northern  Lights  from  the  pen  of  the  celebrated 
Alexander  von  Humboldt : 2 — 

'  Low  down  in  the  distant  horizon,  about  the  part  of  the 
heavens  which  is  intersected  by  the  magnetic  meridian 
(i.e.  the  point  to  which  the  compass-needle  is  directed), 
the  sky,  which  was  previously  clear,  is  at  once  overcast. 
A  dense  wall  or  bank  of  cloud  seems  to  rise  higher  and 
higher,  until  it  attains  an  elevation  of  8  or  10  degrees. 
The  colour  of  the  dark  segment  passes  into  brown  or 
violet,  and  stars  are  visible  through  the  smoky  stratum, 
as  when  a  dense  smoke  darkens  the  sky.  A  broad, 
brightly  luminous  arch,  first  white,  then  yellow,  encircles 
the  dark  segment.  .  .  .  The  luminous  arch  remains  some- 
times for  hours  together,  flashing  and  kindling  in  ever- 
varying  undulations  before  rays  and  streamers  emanate 
from  it  and  shoot  up  to  the  zenith.  The  more  intense 
the  discharge  of  the  northern  light,  the  more  bright  is  the 
play  of  colours,  through  all  the  varying  gradations  from 
violet  and  bluish-white  to  green  and  crimson.  The  mag- 
netic columns  of  flame  rise  either  singly  from  the  luminous 

1  Philosophical  Transactions,  Iviii. 

2  Cosmos  (Bohn's  edit.),  vol.  i.  p.  189. 


THE  AURORA  BOREALIS  207 

arch,  blended  with  black  rays  similar  to  thick  smoke,  or 
simultaneously  in  many  opposite  points  of  the  horizon, 
uniting  together  to  form  a  flickering  sea  of  flame,  whose 
brilliant  beauty  admits  of  no  adequate  description,  as  the 
luminous  waves  are  every  moment  assuming  new  and 
varying  forms.  Round  the  point  in  the  vault  of  heaven 
which  corresponds  to  the  direction  of  the  inclination  of 
the  needle,  the  beams  unite  together  to  form  the  corona — 
the  crown  of  the  northern  light — which  encircles  the 
summit  of  the  heavenly  canopy  with  a  milder  radiance 
and  unflickering  emanations  of  light.  It  is  only  in  rare 
instances  that  a  perfect  crown  or  circle  is  formed;  but, 
on  its  completion,  the  phenomenon  has  invariably  reached 
its  maximum,  and  the  radiations  become  less  frequent, 
shorter,  and  more  colourless.  The  crown  and  the  luminous 
arches  break  up,  and  the  whole  vault  of  heaven  becomes 
covered  with  irregularly  scattered  broad,  faint,  almost 
ashy  grey,  luminous,  immovable  patches,  which  in  their 
turn  disappear,  leaving  nothing  but  a  trace  of  the  dark 
smoke-like  segment  on  the  horizon.  There  often  remains 
nothing  of  the  whole  spectacle  but  a  white,  delicate  cloud, 
with  feathery  edges,  or  divided  at  equal  distances  into 
small  roundish  groups,  like  cirro-cumuli/ 

These  phenomena    are  also  visible  in  the  Southern 
hemisphere,  and  are  produced  by  the  Aurora  Australis. 

The  luminous  arches  were  also  well  described  by  Mr. 
William  Key  in  a  letter  to  Dr.  Priestley,  published  in  the 
Philosophical  Transactions  for  1783.  He  noticed  that 
the  summit  of  the  arch  passed  near  or  through  the  pole- 
star;  the  arches  were  not  always  accompanied  by  the 
'  dancers.'  Key,  following  Canton  unwittingly,  connected 
the  aurora  with  discharges  of  electricity  through  rarefied 
gases.  His  words  are:  'Let  me  hazard  a  conjecture 
respecting  the  white  colour  and  stationary  appearance  of 
some  of  these  arches.  Experiments  in  electricity,  made 


208    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

with  what  is  called  an  '  exhausted '  receiver,  show  that  the 
colour  and  motion  of  the  electric  spark  vary  in  proportion 
to  the  rarity  of  the  air  in  the  receiver.  The  more  the  air 
is  rarefied,  the  more  movable  and  coloured  is  the  electric 
aura  passing  through  it.  On  the  contrary,  the  colour  of 
the  spark  approaches  to  whiteness,  and  moves  with  greater 
difficulty,  as  the  air  is  admitted.  Will  this  observation 
serve  in  any  measure  to  account  for  the  difference  in 
colour  and  motion  of  these  electrical  arches,  for  such  I 
presume  to  call  them  ?  May  we  not  suppose  the  more 
coloured  and  brilliant  portions  of  the  aurora  borealis  to  be 
made  in  the  rarer  parts  of  the  atmosphere,  while  the  more 
white  and  stationary  ones  possess  the  denser  parts  ?  The 
whitest  arches  which  I  saw  were  the  most  fixed/ 

Repeated  attempts  have  been  made  to  ascertain  the 
height  of  an  aurora.  Henry  Cavendish,  the  celebrated 
chemist,  calculated  the  height  from  the  data  furnished  by 
three  observers  of  an  aurora  which  was  seen  in  1784— one 
of  whom  was  stationed  at  Cambridge,  one  at  Kimbolton 
in  Huntingdonshire,  and  one  at  Blockley  in  Gloucester- 
shire— by  simple  trigonometry,  knowing  the  angle  which 
the  summit  of  the  arch  appeared  to  subtend  with  the 
horizon  in  each  case ;  the  results  are  very  reasonably  con- 
cordant, and  give  an  altitude  of  52  to  71  miles.  Many 
subsequent  attempts  have  been  made,  and  with  similar 
results.  One  of  the  latest  writers,  Professor  Birkeland, 
of  Christiania,  gives  as  limits  62  to  124  miles  (100-200 
kilometres).  The  difficulty  in  such  observations  is  to 
make  sure  that  the  observers  in  different  places  have 
been  measuring  the  same  arch  at  the  same  moment.  I 
shall  have  occasion  later  to  bring  evidence  of  a  totally 
different  character  to  confirm  the  general  accuracy  of  such 
measurements. 

Between  the  years  1786  and  1793  John  Dalton,  who 
was  as  indefatigable  a  meteorologist  as  he  was  a  distin- 


THE  AURORA  BOREALIS  209 

guished  chemist,  observed,  from  Kendal  and  Keswick,  in 
Cumberland,  no  fewer  than  250  displays  of  northern 
lights ;  he  established  the  fact  that  the  highest  part  of  the 
luminous  arc  lies  exactly  above  the  magnetic  pole,  and 
that  the  streamers  are  parallel,  at  least '  over  a  moderate 
extent  of  country,'  with  the  compass-needle  as  it  dips 
towards  the  magnetic  pole,  which  is  believed  to  exist  in 
the  north  of  Canada,  within  the  Arctic  circle. 

The  celebrated  De  la  Rive,  of  Geneva,  made  an  attempt 
to  reproduce  the  aurora  in  the  interior  of  a  glass  vessel.1 
He  started  from  the  fact  that  the  atmosphere  is  always 
charged  with  positive  electricity,  and  that  the  earth  is 
negatively  electrified ;  he  presumed,  accordingly,  that  the 
two  kinds  of  electricity  would  neutralise  one  another,  and 
that  currents  would,  as  a  rule,  rise  vertically  to  the  earth's 
surface.  Neutralisation  occurs  slowly  when  rain  or  snow 
falls,  and  suddenly  when  lightning  flashes.  De  la  Rive's 
theory  is  that  in  the  upper  regions  of  the  atmosphere 
electric  currents  circulate  from  the  equator  to  the  two 
poles ;  and  terrestrial  currents,  in  the  interior  of  the  earth, 
are  continually  flowing  from  the  poles  towards  the 
equator.  Conduction,  he  thought,  would  be  easier  in  the 
higher  than  in  the  lower  regions  of  the  atmosphere,  and 
also  better  at  the  poles  than  near  the  equator,  because  of 
the  moisture  and  frequent  mists  in  the  polar  atmosphere. 
The  discharge  through  the  polar  air  would,  he  believed, 
render  the  mist  luminous,  and  thus  produce  the  pheno- 
mena already  described. 

His  apparatus,  which  I  had  the  good  fortune  to  see  in 
September  1902  at  Geneva,  consisted  of  a  globe  with  a 
neck  at  each  '  pole.'  Through  one  of  these  necks  passed 
a  copper  rod  A,  one  end  of  which  was  connected  with  the 
positive  discharge  of  an  electrical  machine ;  at  the  other 
end  a  ring  of  copper  B  was  attached.  G  is  an  insulated 

1  Memoires  de  la  Soc.  de  Phys.  et  d  'His.  Nat.  de  Geneve,  vol.  xiii. 

O 


210    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

soft-iron  bar  covered  with  an  insulating  composition,  and 
projecting  through  the  opposite  neck  of  the  flask.  By 
touching  the  exposed  end  of  this  rod  with  an  electro- 


DE  LA  RIVE'S  APPARATUS  FOR  REPRODUCING  THE  AURORA 

magnet  D,  it  also  became  a  magnet.  The  air  in  the  globe 
having  been  rarefied,  a  brush  discharge  took  place  between 
the  ring  B  and  the  end  of  the  rod  (7;  on  making  C  a 
magnet,  the  discharge  became  more  luminous  and  regular, 
and  revolved  round  the  magnet,  sending  streamers  towards 
the'  end  of  the  rod.  In  De  la  Rive's  model  the  copper 
ring  represents  the  atmosphere,  from  which  electricity 
discharges  to  the  rod  C,  representing  the  earth.  He  con- 
cluded that  the  aurora  forms  a  luminous  ring  round  the 
magnetic  poles  as  centres,  with  a  greater  or  less  diameter, 
the  ring  rotating  on  account  of  the  earth's  magnetism; 
that  it  is  due  to  a  discharge  from  the  positively  electrified 
atmosphere  to  the  negatively  electrified  earth,  the  separa- 
tion of  the  two  kinds  of  electricity  being  caused  by  the 
action  of  the  sun,  chiefly  in  equatorial  regions;  that 
discharges  are  of  constant  occurrence,  though  with  very 
varying  intensities,  and  that  the  cirro-cumulus  clouds  are 
also  illuminated  by  such  discharges. 

When  the  spectroscope  was  turned  on  the  aurora  the 
presence  of  a  green  line  of  wave-length  about  5570  units 


THE  AURORA  BOREALIS  211 

was  noticed.  Different  observers  gave : — Angstrom,  5568  ; 
Vogel,  5572;  Vijkander,  5573;  Lemstrom,  5570;  Huggins, 
5570-4;  Copeland,  5573;  Gyllenskjold,  5569;  Campbell, 
5571-6;  Sykera,  5570;  the  Danish  Mission  to  Iceland  in 
1899-1900,  5570.  Many  other  lines  have  been  photo- 
graphed, of  which  more  hereafter ;  but  this  line  is  extra- 
ordinarily intense,  and,  indeed,  can  often  be  seen  when 
there  is  no  visible  aurora  by  simply  directing  a  pocket 
spectroscope  towards  the  north.  The  line  when  first 
observed  was  not  known  to  be  characteristic  of  the 
spectrum  of  any  element. 

In  1898  I  had  the  honour  to  announce  to  the  Royal 
Society  the  discovery,  in  conjunction  with  my  assistant, 
Dr.  M.  W.  Travers,  of  the  existence  of  three  new  elemen- 
tary substances  in  the  atmosphere,  to  which  we  gave  the 
names — neon,  or  '  the  new  one ' ;  krypton,  or  '  the  hidden 
one ' ;  and  xenon,  or  '  the  stranger.' 

The  spectrum  of  neon  is  characterised  by  many  lines 
in  the  red,  orange,  and  yellow ;  while  that  of  xenon 
shows  many  green  and  blue  lines.  The  light  evolved 
from  tubes  containing  these  gases  under  low  pressure 
when  an  electric  'current  of  high  tension  is  passed  through 
them,  is  of  a  corresponding  hue ;  thus  neon  sends  out  a 
splendid  rose  or  flame-coloured  light ;  and  xenon,  a  sky- 
blue  ;  while  the  light  of  krypton  is  nearly  white,  although 
seen  by  some  of  a  pale  lilac,  and  by  others  of  a  pale-green 
colour. 

The  densities  of  the  elements  proved  to  be  as  had  been 
expected :  that  of  neon,  compared  with  hydrogen  taken  as 
2,  is  20 ;  of  krypton,  82 ;  and  of  xenon,  128. 

Shortly  after  the  discovery  of  krypton,  my  assistant, 
Mr.  Baly,  measured  carefully  the  wave-lengths  of  its  more 
important  lines ;  and  one  of  these,  a  very  brilliant  green 
line,  had  the  wave-length  5570*5.  The  day  after  this 
was  published,  Sir  William  Huggins  wrote  me  privately 


212    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

pointing  out  the  identity  of  this  wave-length  with  the 
principal  auroral  line ;  and  a  week  later,  Professor  Arthur 
Schuster,  in  a  letter  to  Nature,  called  attention  to  the 
same  coincidence. 

It  therefore  appeared  probable  that  the  aurora  might 
be  produced  by  electric  discharges  in  the  upper  atmo- 
sphere, through  a  gas  in  which  krypton  was  present  in 
considerable  amount. 

In  the  meantime  Professor  Paulsen,  of  Copenhagen, 
has  been  examining  the  photographed  spectra  of  the 
aurora  collected  by  the  Icelandic  and  Finland  expeditions; 
and  it  appears  probable  that  many  of  the  lines  seen  in  the 
auroral  spectrum  are  identical  with  those  of  the  common 
gas  nitrogen,  seen  at  the  cathode  terminal  of  a  vacuum- 
tube.  Professor  Paulsen  has  had  the  great  kindness  to 
send  me  prints  of  two  photographs,  the  lines  of  which  are 
numbered  I.  and  II.  in  the  following  table.  I  have  added 
in  a  parallel  column  the  corresponding  wave-lengths  of 
krypton  lines. 

Lines  of  auroral  and  of  cathode  Lines  of 

nitrogen  spectrum.  krypton.         Intensity. 

I.  II. 

1  Absent.      3140 

2  „        3160 

3  „        3370 

4  Absent.      3540 

5  3580       3580       3590      7 

c  3718     10 

6  3710      Absent.    <  3719      8 

I  3721  7 

7  3760       3760  3754  5 

8  3800       3800  3805  4 

9  3920       3920  3920  8 

f  3995      6 


10    400°       *00     I  3998      5 


THE  AURORA  BOREALIS  213 

Lines  of  auroral  and  cathode  Lines  of 

nitrogen  spectrum.  krypton.         Intensity. 

I.  II. 

11  4060  4060  4057  8 

12  4260  4260  4274  8 

13  5570  Absent.  5570  10 

The  last  is  the  characteristic  line  of  the  aurora,  and  is  one 
of  the  two  brilliant  lines  of  the  krypton  spectrum;  the 
other  brilliant  krypton  line  is  in  the  yellow,  and  cannot 
be  easily  photographed  when  the  light  is  not  bright  but 
flickering,  as  the  auroral  light  is. 

I  ain  not  able  to  decide  yet  whether  the  lines  are  all 
due  to  krypton  or  to  the  cathode  spectrum  of  nitrogen. 
Certainly  there  is  a  striking  similarity  between  the 
nitrogen  spectrum  and  that  of  the  aurora ;  and,  on  the 
other  hand,  the  lines  of  krypton,  though  sufficiently 
coincident  with  those  of  the  aurora  to  satisfy  criticism, 
leave  other  bright  lines  of  the  krypton  spectrum  un- 
accounted for.  Yet  the  cathode  spectrum  of  nitrogen 
does  not  contain  the  line  5570,  the  most  brilliant  of  the 
auroral  spectrum,  and  the  one  most  easily  discovered  by 
aid  of  a  pocket  spectroscope.  Experiments  on  this  matter 
are  not  yet  decisive. 

Moreover,  it  appears  improbable  that  the  aurora  should 
always  exhibit  only  one  spectrum.  The  discharge  of 
electricity  through  a  mixture  of  gases  reveals  more  or  less 
completely  the  spectrum  of  each.  Those  gases  which  are 
present  in  smallest  amount  have,  as  a  rule,  their  spectra 
proportionately  enfeebled.  But  it  does  not  always  happen 
that  all  the  lines  of  the  spectrum  of  any  one  gas  are 
proportionately  enfeebled ;  sometimes  the  character  of  the 
spectrum  itself  is  altered.  The  interposition  of  a  Leiden 
jar  and  a  spark-gap  often  causes  a  radical  alteration  in 
the  spectrum  of  a  gas.  This  can  be  well  seen  with  argon  ; 
when  the  discharge  is  altered,  many  of  the  red  lines  of  the 


214    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

spectrum  disappear  and  blue  lines  become  visible ;  hence 
the  colour  of  the  discharge  changes  from  red  to  blue. 
And  other  gases  exhibit  the  same  kind  of  change,  though 
not  generally  in  so  striking  a  manner.  Further,  it  has 
been  shown  by  my  colleague,  Dr.  Collie,  that  an  element 
may  develop  a  new  and  strong  line  in  its  spectrum 
on  being  mixed  with  a  certain  gas,  which  it  does  not 
exhibit  if  another  gas  be  substituted.  All  these  questions 
are  very  obscure,  and  have  not  as  yet  been  investigated ; 
only  the  fringe  of  the  subject  has  been  touched.  As  the 
aurora,  without  doubt,  is  visible  on  different  occasions  at 
very  different  altitudes,  it  is  more  than  possible  that  the 
spectra  will  differ.  The  appearance  of  red  auroras  would 
imply  a  spectrum  in  which  red  lines  predominate ;  but  I 
am  not  aware  of  any  observation  having  been  made  of  the 
spectrum  of  a  red  aurora.  From  the  similarity  of  colour 
it  might  well  be  conjectured  that  the  red  tint  is  due  to 
the  discharge  occurring  through  an  atmosphere  compara- 
tively rich  in  neon. 

Assuming  for  the  moment  the  identity  of  the  line  of 
wave-length  5570  with  that  of  krypton,  two  questions  at 
once  suggest  themselves.  First,  why  should  this  line  be 
so  remarkably  brilliant  when  krypton  is  present  in  the 
atmosphere  in  comparatively  very  minute  amount  ? 
What  are  the  relative  intensities  of  the  spectra  of  krypton 
and  of  other  gases  under  similar  circumstances  ?  And 
second,  is  there  any  process  which  will  tend  to  increase 
the  relative  amount  of  krypton  in  the  upper  regions  of 
the  atmosphere  ?  I  have  attempted  to  answer  both  these 
questions. 

Some  years  ago,  in  conjunction  with  Professor  Collie, 

experiments  were  made  on  the  visibility  of  the  spectrum 

of  one  gas  in  presence  of  another  with  which  it  was 

diluted.1    The  results  are  given  in  the  following  table: — 

1  Proc.  Roy.  Soc.,  lix.  257. 


THE  AURORA  BOREALIS  215 

AMOUNT   OF   GAS   DETECTABLE   IN  A  MIXTURE 

1.  Helium  in  hydrogen,  10  per  cent,  of  helium  barely  visible. 

2.  Hydrogen  in  helium,    O'OOl  ,,  of  hydrogen  visible. 

3.  Nitrogen  in  helium,      O'Ol  „  of  nitrogen  almost  invisible. 

4.  Helium  in  nitrogen,    10  „  of  helium  difficult  to  detect. 

5.  Argon  in  helium,          0'06  „  still  visible. 

6.  Helium  in  argon,        25  „  invisible. 

7.  Nitrogen  in  argon,        0'08  „  just  visible. 

8.  Argon  m  nitrogen,      37  „  barely  visible. 

9.  Argon  in  oxygen,          2 '3  ,,  difficult  to  distinguish. 

This  table  shows  the  enormous  differences  which  exist 
between  the  behaviour  of  different  gases.  To  take  the 
extreme  cases — while  it  is  possible  to  detect  1  part  of 
hydrogen  in  100,000  of  helium,  it  is  barely  possible  to 
recognise  1  part  of  argon  in  2  of  nitrogen. 

Similar  experiments  with  krypton  showed  that 
In  air,  1  part  of  krypton  is  visible  in       7,100  parts. 

In  oxygen,     1  „  „  „  1,250,000      „ 

In  hydrogen,!  „  „  67      „ 

In  argon,        1          „  „  „  7,150 

In  helium,      1          „  „  „ '          2,860,000      „ 

The  pressure  of  krypton,  too,  in  the  case  of  air  is  almost 
inconceivably  low ;  it  amounts  to  only  one  thirty-millionth 
of  the  usual  atmospheric  pressure.  This  shows  the  enor- 
mous persistency  of  the  krypton  spectrum — that  is,  of  the 
most  conspicuous  line,  the  auroral  green,  for  that  was  the 
one  observed  in  all  instances.  If,  then,  an  electric  dis- 
charge passes  through  the  upper  and  rarefied  strata  of  the 
atmosphere,  the  probability  of  detecting  the  green  line  of 
krypton  will  be  much  greater  than  that  of  detecting  the 
spectrum  of  any  other  element,  even  though  the  latter 
be  present  in  enormously  greater  proportion.  Hydrogen 
alone  has  any  marked  power  of  extinguishing  the  spectrum 
of  krypton. 

It  is  possible  to  calculate  the  maximum  height  of  the 
aurora,  on  the  supposition  that  the  krypton  line  is  no 


216    ESSAYS  BIOGEAPHICAL  AND  CHEMICAL 

longer  visible  when  the  pressure  falls  below  0*000035 
millimetre — the  pressure  observed  when,  in  a  mixture  of 
krypton  and  helium,  the  green  line  of  krypton  became 
very  faint  and  almost  invisible.  Neglecting  the  influence 
of  temperature,  the  pressure  of  the  atmosphere  can  be 
made  to  give  its  height  by  the  formula — 

H  =  18-382  (log.  B-log.  b)  kilometres. 
Substituting  for  B  (barometer)  its  normal  height,  760 
millimetres,  and  for  b  the  pressure  of  the  krypton,  0-000035 
millimetre,  we  have  height  =  135  kilometres,  or  about  84 
miles.  This  number  is  reasonably  near  the  figures  given 
by  Cavendish  and  others.  Professor  Birkeland,  the  latest 
authority,  it  will  be  remembered,  thinks  the  altitude  is 
from  100  to  200  kilometres,1  or  from  62*5  to  125  miles. 

We  may  next  ask — Since  the  spectrum  of  krypton  is 
so  persistent,  why  is  it  not  visible  in  air  ?  The  answer  is 
— Because  the  presence  of  nitrogen  renders  it  invisible, 
for  it  is  not  possible  to  distinguish  less  than  one  part  of 
krypton  by  volume  in  7100  parts  of  air.  But  krypton 
does  not  show  its  spectrum  in  argon,  which  may  be  said 
to  constitute  about  1  per  cent,  of  the  volume  of  air.  Now 
7100  parts  of  air  will  yield  about  70  parts  of  argon,  and  it 
should  be  possible  to  distinguish  the  krypton  line  if  the 
amount  of  krypton  present  we»e  O'Ol  part,  or  1  part  in 
7000.  This  would  give,  for  the  proportion  of  krypton 
in  air,  1  part  in  700,000.  Recent  experiments,  have 
shown  that  it  is  possible  to  extract  1  part  of  krypton 
from  about  7,000,000  of  air ;  and  of  xenon,  which,  owing 
to  its  lower  vapour  pressure,  can  be  extracted  from  air 
with  more  ease  than  krypton,  there  is  only  about  1  part 
in  40,000,000  of  air.  It  is  therefore  clear  why  the  spec- 
trum of  krypton  is  not  visible  in  that  of  crude  argon. 

We  come  next  to  the  question — Is  there  any  reason 
to  believe  that  krypton  may  concentrate  in  the  higher 

1  Expedition  Norv&gienne,  Christiania,  1901,  p.  28. 


THE  AURORA  BOREALIS  217 

regions  of  the  atmosphere,  that  is,  that  its  proportion, 
relatively  to  that  of  the  more  abundant  gases  oxygen  and 
nitrogen,  may  increase  as  the  altitude  grows  greater  ?  To 
this,  I  think,  an  affirmative  answer  may  be  given.  Let  us 
consider  the  grounds  for  the  supposition. 

When  a  gas  is  compressed  it  turns  warm,  as  every  one 
knows  who  has  used  a  bicycle-pump.  Conversely,  when 
it  escapes  from  compression  it  cools  itself.  But  all  gases 
do  not  heat  or  cool  equally  for  equal  amounts  of  compres- 
sion or  expansion ;  for  some  gases  are  raised  to  a  higher 
temperature  than  others  by  absorbing  the  same  quantity 
of  heat;  and  the  same  quantity  of  heat  is,  practically, 
generated  by  the  same  degree  of  compression,  or  absorbed 
by  the  same  degree  of  expansion;  for  work  is  quanti- 
tatively equivalent  to  heat,  as  was  shown  by  Joule  half  a 
century  ago.  Now  40  grams  of  argon  should,  if  the 
specific  heat  of  that  gas  were  the  same  as  that  of  oxygen, 
require  the  same  amount  of  heat  to  raise  its  temperature 
through  1  degree ;  or  put  in  another  way,  if  each  of  these 
gases  were  expanded  to  the  same  amount,  they  would  be 
equally  cooled,  if  equal  amounts  of  heat  were  requisite  to 
raise  their  temperatures  through  an  equal  number  of 
degrees.  But  this  is  not  the  case.  Argon  requires  less 
heat  to  raise  its  temperature  than  oxygen,  in  the  ratio  of 
3  to  5  if  it  is  not  allowed  to  expand,  or  in  the  ratio 
of  5  to  7  if  expansion  is  possible  under  constant  pressure. 
If  allowed  to  expand  under  circumstances  in  which  volume 
increases  while  pressure  falls,  some  ratio  intermediate 
between  these  would  show  the  difference  in  cooling ;  the 
exact  amount  depending  on  the  degree  of  expansion  in 
question.  Broadly  stated,  argon,  in  expanding  will  cool 
itself  considerably  more  than  oxygen  or  nitrogen ;  while  its 
congeners,  helium,  neon,  krypton,  and  xenon,  will  exhibit 
a  degree  of  cooling  practically  identical  with  that  of  argon. 

The  next  point  to  be  considered  is  that  gases  diffuse 


218    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

freely  into  one  another  when  left  in  contact;  so  that  a 
heavy  gas  will  mix  readily  with  a  much  lighter  one,  even 
though  the  heavy  one  may  be  below  and  the  lighter  one 
above.  This  diffusion  results  from  the  motion  of  the 
molecules  of  gases  ;  and  as  the  rate  of  motion  depends  on 
the  temperature  of  the  gas,  those  molecules  which  happen 
to  have  a  high  temperature  move  much  more  rapidly  than 
those  with  a  lower.  When  two  gases  mix,  however,  or 
when  a  hot  gas  mixes  with  a  cold  one,  the  more  rapidly 
moving,  and  therefore  hot,  molecules  very  rapidly  com- 
municate their  motion  to  the  colder  gas,  raising  its 
temperature  until  the  temperatures  of  both  sets  of  mole- 
cules are  equalised.  This  is  due  to  the  enormous  number 
of  encounters  which  take  place  between  the  molecules, 
partly  on  account  of  the  minute  size  of  each  molecule, 
and  the  consequent  number  in  even  a  very  small  volume  ; 
and  partly  to  the  great  rate  at  which  they  are  moving. 
For  example,  it  can  be  calculated  that  in  all  probability 
there  are  50,000,000,000,000,000  or  50  quadrillion  mole- 
cules of  hydrogen  in  a  cubic  millimetre  of  that  gas  (about 
the  volume  of  the  head  of  a  large  pin)  and  that  the 
average  velocity  of  each  molecule  is  at  the  rate  of  4J  miles 
per  second.  No  wonder,  therefore,  that  the  exchange 
between  molecules  of  different  temperature  is  almost 
instantaneous.  It  must  nevertheless  be  borne  in  mind 
that  hot  gases  diffuse  much  more  rapidly  than  cold  ones. 
The  densities  of  the  gases  constituting  the  atmosphere 
are  as  follows,  the  standard  being  that  of  oxygen  taken  as 
16:- 


Water  Vapour,      9  0-333  Neon,        10  0-316 

Nitrogen,  14  0'287  Argon,       20  0'224 

Oxygen,  16  0'250  Krypton,   41  0156 

Carbon  Dioxide,  22  0*213  Xenon,       64  0125 

Helium,  2  0'707  - 


THE  AURORA  BOREALIS  219 

The  relative  rates  of  diffusion  are  inversely  as  the 
square  roots  of  the  densities,  and  are  given  in  the  second 
column.  For  example,  oxygen  escapes  into  a  neighbour- 
ing layer  twice  as  quickly  as  xenon ;  and  helium  nearly 
three  times  as  fast  as  oxygen.  Now  it  is  evident  that  the 
gases  which  will  escape  most  slowly  are  krypton  and 
xenon;  carbon  dioxide  and  argon  come  next  in  order; 
while  nitrogen,  neon,  water  vapour,  and  helium  escape 
more  rapidly  in  the  order  given.  If  then  a  jar  with 
porous  walls  were  full  of  air,  and  were  exposed  to  some 
indifferent  atmosphere,  the  gas  remaining  in  the  jar  after 
some  time  would  contain  more  of  the  heavier  and  less  of 
thelighter  gases  proportionally  to  the  original  amounts 
present. 

The  third  premiss  in  the  argument  is  that  in  equatorial 
regions  there  is  an  upward  current  of  air,  due  to  the 
warming  of  the  earth  by  the  nearly  vertical  rays  of  the 
sun  and  the  consequent  expansion  of  the  air  in  contact 
with  the  soil  or  the  sea ;  while  in  the  polar  regions  there 
is  a  continual  downward  current,  produced  by  the  cooling 
of  the  air  in  contact  with  the  ice  of  the  polar  caps.  This 
circulation  of  the  atmosphere  was  investigated  by  Professor 
James  Thomson  in  1857,  and  his  Bakerian  lecture  on  the 
subject  appeared  in  the  Philosophical  Transactions  for 
1892,  p.  653.  The  conclusion  to  which  he  came  is  that 
the  upward  atmospheric  current  at  the  equator  on  reaching 
the  higher  regions  of  the  atmosphere,  divides  into  two, 
and  while  one  part  of  the  air  travels  in  a  north-easterly 
direction,  the  other  half  travels  in  a  south-easterly  direction 
towards  the  north  and  south  poles  respectively.  Arrived 
at  the  neighbourhood  of  the  polar  caps,  the  air  descends 
and,  broadly  stated,  travels  back  near  the  surface  of  the 
earth  again  towards  the  equator.  We  need  not  here  regard 
eddies  which  occur  near  the  tropics  of  Cancer  and  Capri- 
corn ;  the  main  features  are  sufficient  for  our  purpose. 


220    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

The  air,  then,  as  it  ascends  from  equatorial  latitudes 
cools  itself  in  the  process ;  and  from  what  has  been  said, 
it  would  seem  that  gases  of  the  argon  group  would  cool 
more  rapidly  than  the  other  atmospheric  gases,  oxygen 
and  nitrogen.  Pour  prdciser  les  idtes,  as  the  French  say, 
let  us  confine  our  attention  to  the  northern  hemisphere, 
and  let  us  suppose  that  a  vertical  partition  has  been  set 
up  in  the  neighbourhood  of  the  equator,  quite  permeable 
to  gases,  and  surrounding  the  earth  much  as  the  wooden 
frame  of  a  terrestrial  globe  surrounds  the  globe.  Indeed, 
if  we  conceive  of  that  frame  as  a  double  one,  and  the 
ascending  current  rising  between  the  walls,  we  shall 
realise  what  is  intended.  As  the  upward  current  gains  in 
height,  it  falls  in  temperature ;  and  during  the  whole  of 
the  ascent  the  nitrogen  and  oxygen  are  passing  through 
the  porous  diaphragm  at  a  rate  greater  than  that  of  the 
argon  gases.  With  increasing  height  the  density  of  all 
gases  decreases ;  their  molecules  are  more  widely  separated 
from  each  other,  and  interchange  of  velocity  or,  what  is 
equivalent,  interchange  of  temperature  becomes  less  rapid ; 
hence  the  separation  should  be  a  more  perfect  one  the 
greater  the  altitude.  But,  at  the  same  time,  the  argon 
gases  are  not  wholly  left  in  the  upward  current;  many 
molecules  will  pass  the  barrier;  why  should  they  not 
return  in  as  great  number  as  they  pass  ?  Because  after 
passing  the  partition  they  no  longer  move  upwards  with 
the  same  velocity  as  before;  the  farther  they  progress 
towards  the  north  the  less  inducement  to  rise,  for  the 
temperature  of  the  earth  is  lower. 

This  reasoning  is  equally  applicable  if  we  regard  the 
barrier  as  removed ;  we  may  mentally  surround  the  earth 
with  an  infinity  of  such  barrier  rings,  parallel  to  the  plane 
of  the  equator ;  and  it  will  still  remain  true  that  the 
warmer  gases  will  tend  to  escape  in  the  lower  regions 
of  the  atmosphere,  leaving  the  cooler  gases  to  ascend. 


THE  AURORA  BOREALIS  221 

At  the  poles  the  process  is  reversed.  The  argon  gases 
are  more  heated  during  their  descent  than  the  oxygen  and 
nitrogen,  and  will  escape  into  neighbouring  layers  of 
atmosphere  at  a  greater  altitude,  on  the  average,  than  the 
latter.  The  relative  rates  of  diffusion  of  these  gases,  too, 
may  play  an  even  more  important  part  in  effecting  the 
separation ;  the  heaviest — argon,  carbon  dioxide,  krypton, 
and  xenon — will  remain  in  the  ascending  layer  in  larger 
relative  proportion  than  the  oxygen,  nitrogen,  and  other 
lighter  gases,  and  will,  therefore,  be  carried  to  the  upper 
regions  of  the  atmosphere  by  the  ascending  equatorial 
current ;  but  in  the  descending  polar  current  the  process 
would  be  reversed,  for  the  heavier  gases  would  be  carried 
down  in  the  current  with  less  escape  than  the  lighter 
ones.  The  effect  of  diffusion  alone,  neglecting  the  heating 
or  cooling  of  the  gases,  would,  therefore,  be  neutralised 
during  each  complete  circulation. 

But  the  process  of  separation  which  depends  on  the 
difference  of  temperature  of  the  gases,  were  there  only  one 
circulation,  would  in  all  probability  be  productive  of  very 
small  result;  it  is  to  be  observed,  however,  that  the  effect 
is  cumulative,  that  the  process  of  concentration  of  the 
argon  gases  in  the  higher  regions  of  the  atmosphere  goes 
on  from  age  to  age,  and  that  there  may  now  be  an 
apparently  stationary  state,  when  separation  of  argon 
gases  from  oxygen  and  nitrogen  balances  mixture  by 
diffusion  and  the  mixing  which  inevitably  accompanies 
winds.  It  may  be  suggested  that  the  greater  frequency 
of  auroras  during  years  when  the  sunspots  are  large  and 
easily  visible  may  be  connected  with  the  higher  tempera- 
ture of  such  years,  as  well  as  with  the  magnetic  disturb- 
ances which  invariably  accompany  sunspots. 

To  sum  up : — 1.  The  gases  of  the  argon  group  are  more 
easily  heated  and  cooled  than  are  oxygen  and  nitrogen, 
2.  They  are  cooled  more  than  the  latter  during  their 


222    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

upward  ascent  at  the  equator,  and  therefore  tend  to  con- 
centrate in  the  ascending  current  as  it  reaches  the  con- 
fines of  the  atmosphere,  owing  to  the  more  rapid  escape 
of  oxygen  and  nitrogen  by  diffusion.  3.  The  phenomena 
are  reversed  in  the  descending  currents  at  the  poles,  and 
the  argon  gases  tend  to  mix  with  neighbouring  layers  of 
gas  at  high  altitudes.  4.  The  higher  strata  of  the  atmo- 
sphere are  probably  richer  in  the  inactive  gases  than  the 
lower  strata. 

As  electric  discharges  producing  the  aurora  certainly 
occur  at  great  altitudes,  the  spectra  seen  are  those  of  the 
inactive  gases;  and  owing  to  the  fact  that  the  krypton 
green  line,  of  wave-length  5570  units,,  is  remarkably  easily 
visible,  even  in  an  admixture  of  other  gases,  it  happens  to 
be  the  most  conspicuous  line  in  the  auroral  spectrum. 

This  leads  us  to  consider,  in  the  last  place,  the  cause  of 
the  electric  current.  And  here  we  enter  on  a  different 
region  of  thought. 

There  are  two  theories  on  the  subject,  one  due  to  Pro- 
fessor Birkeland,1  of  Christiania,  the  other  to  Professor 
Arrhenius,2  of  Stockholm.  It  has  long  been  known  that 
violet  light  rays  and  the  invisible  rays  of  the  spectrum 
beyond  the  violet,  which  can  be  detected  by  photography, 
have  the  property  of  discharging  a  negatively  electrified 
body.  It  is  suggested  by  Professor  Birkeland  that  the 
spots  on  the  sun  are  caused  by  solar  eruptions,  or,  to  use  a 
familiar  word,  volcanoes ;  and  that  the  sun  then  emits 
negatively  charged  corpuscles,  similar  to  those  which  are 
believed  to  constitute,  partly  at  least,  the  cathode  rays — 
rays  producing  those  utilised  for  surgical  practice  in  taking 
photographs  of  bones.  Birkeland  supposes  that  such 
corpuscles  are  '  sucked  in  '  to  the  earth's  magnetic  poles, 
giving  rise  to  vortices  of  electric  currents  in  the  upper 

1  Archives  des  Sciences  Phys.  et  Nat.  tie  Geneve,  June  1896. 

2  Physikalische  Zeitschrift,  ii.  Nos.  6  and  7. 


THE  AURORA  BOREALIS  223 

regions  of  the  atmosphere.  It  is  indeed  known  that  such 
rays  are  deviated  by  the  neighbourhood  of  a  magnet ;  and 
also  that  the  presence  of  large  solar  spots  is  always 
accompanied  by  magnetic  '  storms '  on  the  earth  and  the 
appearance  of  frequent  and  brilliant  auroras. 

The  theory  of  Arrhenius  is  that  the  corpuscles  emitted 
by  the  sun  are  not  inconceivably  minute  bodies,  but  have 
an  appreciable  size ;  that  they  are,  say,  the  thousandth  of 
a  millimetre,  or  the  25,000th  of  an  inch  in  diameter,  and 
that  they  are  expelled  from  the  sun  by  the  repulsive 
action  of  light. 

Whichever  theory  be  correct,  it  is  probable  that  nega- 
tively electrified  gaseous  molecules  are  present  in  the 
upper  regions  of  the  atmosphere,  and  it  is  also  probable 
that  these  molecules  receive  their  charge  most  readily 
where  they  are  most  exposed  to  a  vertical  sun,  that  is,  at 
and  near  the  equator.  We  have  seen  that  Professor  James 
Thomson's  upper  aerial  currents  would  carry  these  and 
other  molecules  towards  the  poles;  they  would  move 
spirally  northwards  and  southwards  with  an  easterly 
trend.  As  they  approach  the  poles  their  number  per  unit 
area  will  obviously  increase ;  for  the  terrestrial  parallels  of 
latitude  decrease  in  circumference  the  nearer  they  are  to 
the  poles.  It  is  to  be  expected  that  before  the  actual  poles 
are  reached,  the  potential  of  the  upper  air  should  increase 
to  such  an  extent  as  to  produce  a  luminous  discharge,  in 
the  form  of  a  ring  or  halo,  with  the  magnetic  poles  as 
their  centres.  It  is  conceivably  this  ring  which  we  see  as 
an  arch  in  the  sky;  it  may  not  be  so  high-as  the  coloured 
streamers,  and  may  well  give  the  nitrogen  spectrum.  It 
must  be  remembered,  however,  that  the  earth  is  a  huge 
magnet;  and  that  lines  of  force  connect  the  poles  in  a 
fashion  shown  in  the  figure.  The  halo,  exposed  to  these 
magnetic  forces,  will  send  out  streamers  towards  the  poles 
as  well  as  towards  the  zenith;  as  they  approach  the 


224    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

equator,  however,  the  light  will  fade,  owing  to  the  spread- 
ing and  weakening  of  these  lines. 

An  imperfect  attempt  has  been  made  to  imitate  the 
auroral  phenomena,  but  it  nevertheless  shows  in  some 
degree  the  appearance  of  the  northern  lights.  A  globe, 
containing  krypton  at  very  low  pressure,  is  suspended 
between  the  poles  of  a  powerful  electro- magnet ; 1  a  ring, 
consisting  of  five  or  six  coils  of  covered  wire,  is  laid  on 
the  top  of  the  globe,  and  by  help  of  an  induction-coil  and 
a  Leiden  jar,  strong  induction  discharges  are  made  to 
pass  through  the  coil.  Each  discharge  is  accompanied  by 
a  circular  discharge  in  the  interior  of  the  globe.  The 
effect  is  that  of  a  ring  or  halo  near  the  upper  side  of  the 
jar.  On  'making'  the  electro-magnet,  the  ring  sends 
out  streamers,  exactly  similar  in  appearance  to  auroral 
streamers,  and  like  them  they  have  a  rotary  motion  and 
flicker,  shortening  and  lengthening,  just  as  natural 
streamers  do.  If  it  were  possible  to  place  a  magnetic 
model  of  the  earth  inside  such  a  globe,  I  doubt  not  that 
the  streamers  would  follow  directions  similar  to  those  in 
the  figure,  and  that  the  imitation  would  still  more  closely 
resemble  the  reality.  The  light  evolved  from  pure 
krypton,  under  the  influence  of  such  discharges,  is  of  a 
whitish  steel-blue  colour  with  occasional  green  and  lilac 
flickers,  and  it  also  recalls  the  appearance  of  the  natural 
aurora.  But,  as  already  remarked,  it  is  more  than 
probable  that  the  spectrum  of  the  aurora,  seen  at  different 
times  and  in  different  altitudes,  may  show  not  only  the 
spectrum  of  krypton,  but  also  those  of  the  other  atmo- 
spheric gases. 

One  more  remark  before  concluding.  The  temperature 
of  the  upper  atmosphere  is  undoubtedly  very  low  ;  but  at 
such  altitudes  even  xenon,  the  least  volatile  of  the  atmo- 
spheric gases,  possesses  so  high  a  vapour  pressure  that  it 

1  The  electro'inagnet  belonging  to  a  small  1  h.p.  dynamo  was  used. 


DIAGKAM  OF  THE   EARTH   AND  THE   POLAR  AURORAS 


Facing  page  224 


THE  AURORA  BOREALIS  225 

would  certainly  remain  gaseous ;  for  in  order  to  liquefy  or 
solidify  a  gas,  not  merely  reduction  of  temperature,  but 
also  considerable  pressure,  is  required.  It  is,  however, 
quite  possible  that  water-vapour,  in  the  lower  regions 
frequented  by  the  aurora,  may  exist  in  a  supersaturated 
condition,  and  that  the  electric  discharges  may  bring 
about  condensation,  and  on  the  large  scale  of  nature,  as 
on  the  small  scale  of  a  laboratory  experiment,  produce 
mists,  and  so  give  rise  to  the  cirro-cumulus  clouds  which 
so  often  accompany  an  aurora. 

The  solving  of  conundrums  has  for  many  people  a  great 
attraction;  Nature  surrounds  us  with  conundrums,  and 
it  is  one  of  the  greatest  pleasures  in  life  to  attempt 
their  solution.  Whether  or  not  I  have  been  successful 
in  offering  a  partial  solution  of  the  one  which  we  may 
call  the  '  Merry  Dancers,'  time  will  show. 


THE  FUNCTIONS  OF  A  UNIVERSITY 

ORATION   DELIVERED   AT  UNIVERSITY   COLLEGE,   LONDON 
JUNE   6,   1901 

I  AM  about  to  speak  of  the  Functions  of  a  University. 
The  word  University  has  borne  many  significations  ;  and, 
indeed,  its  functions  are  various,  and  the  signification 
attached  to  the  word  has  depended  on  the  particular  point 
of  view  taken  at  the  time.  An  eminent  German,  who 
visited  me  some  years  ago,  made  the  remark  after  seeing 
University  College: — 'Aber,  lieber  Herr  College,  University 
College  ist  eine  kleine  Universitat.'  So  it  is ;  for  it  fulfils 
most  of  the  functions  of  the  most  successful  Universities  in 
the  world.  A  countryman  of  the  gifted  founder  of  this 
College,  Thomas  Campbell,  a  man  who  has  left  even  a 
deeper  mark  than  he  on  the  literature  of  the  world, 

said : — 

'  0  wad  some  Pow'r  the  giftie  gie  us 
To  see  oursels  as  ithers  see  us  ! 5 

Were  that  gift  given  us,  I  am  confident  that  we  should 
have  no  cause  to  blush.  One  of  the  most  necessary 
conditions  of  success  is  confidence  in  oneself — 'a  gude 
consait  of  oursels,'  as  the  Scots  saying  has  it;  and  I 
know  that  learned  men  throughout  the  world  look  on  the 
work  done  at  University  College  as  among  the  best  pro- 
duced. And  why  is  this  ?  Because  the  traditions  of 
University  College  have  always  been  that  it  is  not  merely 
a  place  where  known  facts  and  theories  should  be  ad- 


228    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

ministered  in  daily  doses  to  young  men  and  young  women, 
but  that  the  duty  of  the  professors,  assistant-professors, 
teachers,  and  advanced  students  is  to  increase  knowledge. 
That  is  the  chief  function  of  a  University — to  increase 
knowledge.  But  it  is  not  the  only  one. 

A  University  has  always  been  regarded  as  a  training 
school  for  the  '  learned  professions,'  i.e.  for  Theology,  Law, 
and  Medicine.  The  terms  of  our  charter  have  excluded 
the  first  of  these  branches  of  knowledge.  Founded  as  it 
was  in  the  'twenties,  when  admission  to  Oxford  or  Cam- 
bridge involved  either  belief  in  the  tenets  of  the  Church 
of  England,  or  insincerity,  it  was  not  possible  to  provide 
courses  in  Theology  which  should  be  acceptable  to  Non- 
conformists, Jews,  and  others  who  desired  education.  On 
the  whole,  it  appears  to  me  better  that  a  subject,  about 
which  so  much  difference  of  opinion  exists,  should  be 
taught  in  a  separate  institution.  There  are  many  branches 
of  knowledge  which  can  be  adequately  discussed  without 
intruding  into  any  sphere  of  religious  controversy ;  and, 
indeed,  it  would  be  difficult,  I  imagine,  to  treat  mathe- 
matics or  chemistry  from  a  sectarian  standpoint.  I,  at 
least,  have  never  tried.  There  are  subjects  which  may  be 
placed  on  the  border-line,  for  example,  Philosophy;  but 
such  subjects,  and  they  are  few  in  number,  might  well 
form  part  of  the  curriculum  of  the  theological  college,  if 
thought  desirable.  It  is  a  thousand  pities  that  instead 
of  founding  King's  College,  a  theological  college  had  not 
been  established  in  the  immediate  neighbourhood  of 
University  College ;  it  would  have  strengthened  us,  and  it 
would  have  tended,  too,  to  the  advantage  of  the  Church 
of  England.  However,  what  is  done  can't  be  undone; 
and  let  us  wish  all  prosperity  to  our  sister  college,  and 
a  long  and  useful  life.  We  are  now  friends,  and  have 
been  friends  for  many  years.  May  that  friendship  long 
continue ! 


THE  FUNCTIONS  OF  A  UNIVERSITY       229 

Dismissing  the  Faculty  of  Theology,  therefore,  as  out  of 
our  power,  as  well  as  beyond  our  wishes,  let  us  turn  to  the 
remaining  two  learned  professions.  University  College,  I 
believe,  was  the  first  place  in  England  where  a  systematic 
legal  education  could  be  obtained.  Our  chairs  of  Roman 
Law,  Constitutional  Law,  and  Jurisprudence  were  the  first 
to  be  established  in  England,  although  such  chairs  had 
for  long  been  known  on  the  Continent  and  in  Scotland. 
'  Imitation  is  the  sincerest  flattery ' ;  and  in  the  fulness  of 
time,  the  Inns  of  Court  started  a  school  of  their  own. 
Our  classes,  which  used  to  be  crowded,  dwindled,  and  our 
law-school  is  certainly  not  our  strongest  feature.  I  am 
not  sufficiently  acquainted  with  English  legal  education 
to  pronounce  an  opinion  as  to  whether  methods  of  train- 
ing as  they  at  present  exist  in  England  are  the  most 
effective :  I  have  heard  rumours  that  they  are  not.  That 
must  be  left  to  specialists  to  decide.  But  arguing  from 
the  experience  of  another  faculty,  in  which  the  apprentice- 
ship system  once  existed,  and  which  has  changed  that 
system  with  a  view  to  reform,  and  judging,  too,  from 
experience  abroad  and  in  Scotland,  I  venture  to  think 
that  some  improvement  in  legal  education  is  possible.  If 
that  opinion  is  correct,  it  is  surely  not  too  much  to  hope 
that  the  claims  of  University  College  may  be  considered 
as  having  made  the  first  attempt  to  systematise  legal 
education  in  England. 

The  Faculty  of  Medicine  has  existed  in  a  flourishing  state 
since  the  inception  of  University  College.  Not  long  after 
the  College  was  built,  the  old  Hospital  buildings,  were 
erected.  One  of  my  predecessors,  on  a  similar  occasion  to 
this,  has  given  you  an  entrancing  account  of  the  early 
history  of  this  side  of  the  College,  and  has  discoursed  on 
the  eminent  men  who  filled  the  chairs  in  the  Medical 
Faculty.  Here  young  men  whose  intention  it  is  to  enter 
the  medical  profession  are  trained ;  they  now  receive  five 


230    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

years'  instruction  in  the  various  branches  of  knowledge 
bearing  on  their  important  calling.  I  would  point  out 
that  this  function  of  a  University  is  professedly  a  technical 
one :  the  training  of  medical  men.  True,  many  researches 
have  been  made  by  the  eminent  men  who  have  held 
chairs  in  this  Faculty ;  but  that  is  not  the  primary  duty 
of  such  men ;  their  duty  is  to  train  others  to  exercise  a 
profession.  If  they  advance  their  subject  in  doing  so,  so 
much  the  better ;  it  increases  the  fame  of  the  school,  it 
imparts  enthusiasm  to  their  students,  and  in  many  cases 
their  discoveries  have  been  of  unspeakable  benefit  to  the 
human  race.  In  a  certain  sense,  every  medical  man  is  an 
investigator ;  the  first  essential  is  that  he  shall  be  able  to 
make  a  correct  diagnosis ;  the  next,  that  he  shall  prescribe 
correct  treatment.  But  novelty  is  not  essential ;  few  men 
evolve  new  surgical  operations  or  introduce  new  remedies; 
and  though  we  have  in  the  past  had  not  a  few  such,  they 
are  not  essential  for  a  successful  medical  school,  the  object 
of  which  is  to  train  good  practical  working  physicians  and 
surgeons.  The  teaching  staff  of  the  Medical  Faculty  must 
of  necessity  be  almost  all  engaged  in  practice,  and,  indeed, 
it  would  be  unfortunate  for  their  students  if  they  were 
merely  theoretical  teachers.  Let  me  recapitulate  my 
point:  the  Medical  Faculty  is  essentially  a  technical 
Faculty ;  the  hospital  is  its  workshop. 

In  England,  of  recent  years,  schools  of  engineering 
have  been  attached  to  the  Universities.  Abroad  and  in 
America  they  are  separate  establishments,  and  are  some- 
times attached  to  large  engineering  works,  where  the 
pupils  pursue  their  theoretical  and  practical  studies 
together,  taking  the  former  in  the  morning,  the  latter  in 
the  afternoon.  Here  again  the  subject  is  a  professional 
one.  The  object  of  the  student  is  to  become  a  practical 
engineer,  and  all  his  work  is  necessarily  directed  to  that 
end.  Like  other  workers  in  different  fields,  his  aim  is  the 


THE  FUNCTIONS  OF  A  UNIVERSITY       231 

acquisition  and  utilisation  of  'power/  but  in  his  case  it  is 
his  object  to  direct  mechanical  and  electrical  power  so  as 
to  add  to  the  convenience  of  the  public.  A  machine  is  an 
instrument  for  converting  heat  or  electrical  energy  into 
what  is  termed  '  kinetic  energy,'  and  it  is  with  the  laws 
and  modes  of  this  conversion  that  he  has  to  deal.  Such 
abstract  sciences  as  chemistry,  physics,  and  geology, 
therefore,  are  studied  as  means  to  an  end ;  not  for  their 
own  sakes.  They  afford  him  a  glimpse  of  the  principles 
on  which  his  engineering  practice  is  based ;  and  mathe- 
matics is  essential  in  order  that  he  may  be  able  to  apply 
physical  principles  to  the  practical  problems  of  his  pro- 
fession. 

We  see,  then,  that  a  University,  as  it  at  present  exists, 
provides,  or  may  provide,  technical  instruction  for  theo- 
logians, for  lawyers,  for  medical  men,  and  for  engineers. 
It  is,  in  fact,  an  advanced  technical  school  for  these 
subjects. 

But  it  is  more,  and  I  believe  that  its  chief  function  lies 
in  the  kind  of  work  which  I  shall  attempt  now  to  describe. 
The  German  Universities  possess  what  they  term  a 
'  Philosophical  Faculty ' ;  and  this  phrase  is  to  be  accepted 
in  the  derivational  meaning  of  the  word  —  a  faculty 
which  loves  wisdom  or  learning.  The  watchword  of  the 
members  of  this  faculty  is  Research;  the  searching  out 
the  secrets  of  Nature,  to  use  a  current  phrase ;  or  the 
attempt  to  create  new  knowledge.  The  whole  machinery 
of  the  Philosophical  Faculty  is  devised  to  achieve  this 
end ;  the  selection  of  the  teachers,  the  equipment  of  the 
laboratories  and  libraries,  the  awarding  of  the  degrees. 

What  are  the  advantages  of  research  ?  Much  is  heard 
nowadays  regarding  the  necessity  of  state  provision  for 
its  encouragement,  and  the  Government  places  at  the 
disposal  of  the  Royal  Society  a  sum  of  no  less  than  £4000 
a  year,  which  is  distributed  in  the  form  of  grants  to 


232    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

applicants  who  are  deemed  suitable  by  committees 
appointed  to  consider  their  claims  to  assistance. 

There  are  two  views  regarding  the  advantage  of  research 
which  have  been  held.  The  first  of  these  may  be  termed 
the  utilitarian  view.  You  all  know  the  tale  of  the  man 
of  science  who  was  asked  the  use  of  research,  and  who 
parried  with  the  question — What  is  the  use  of  a  baby  ? 
Well,  I  imagine  that  one  school  of  political  economists 
would  oppose  the  practice  of  child-murder  on  the  ground 
that  potentially  valuable  property  was  being  destroyed. 
These  persons  would  probably  not  be  those  who  stood  to 
the  baby  in  a  parental  relation.  Nor  are  the  most  suc- 
cessful investigators  those  who  pursue  their  inquiries  with 
the  hope  of  profit,  but  for  the  love  of  them.  It  is,  how- 
ever, a  good  thing,  I  believe,  that  the  profanum  vulyus 
should  hold  the  view  that  research  is  remunerative  to  the 
public — as  some  forms  of  it  undoubtedly  are. 

The  second  view  may  be  termed  the  philosophical  one. 
It  is  one  held  by  lovers  of  wisdom  in  all  its  various  forms. 
It  explains  itself,  for  the  human  race  is  differentiated 
from  the  lower  animals  by  the  desire  which  it  has  to  know 
'  why.'  You  may  have  noticed,  as  I  have,  that  one  of  the 
first  words  uttered  by  that  profound  philosopher,  a  small 
child,  is  '  why  ? '  Indeed  it  becomes  wearisome  by  its 
iteration.  We  are  the  superiors  of  the  brutes  in  that  we 
can  hand  down  our  knowledge.  It  may  be  that  some 
animals  also  seek  for  knowledge ;  but  at  best,  it  is  of  use 
to  themselves  alone;  they  cannot  transmit  it  to  their 
posterity,  except  possibly  by  way  of  hereditary  faculties. 
WTe,  on  the  contrary,  can  write  and  read ;  and  this  places 
us,  if  we  like,  in  possession  of  the  accumulated  wisdom  of 
the  ages. 

Now  the  most  important  function,  I  hold,  of  a  Uni- 
versity is  to  attempt  to  answer  that  question  '  why  ? ' 
The  ancients  tried  to  do  so;  but  they  had  not  learned 


THE  FUNCTIONS  OF  A  UNIVERSITY       233 

that  its  answer  must  be  preceded  by  the  answer  to  the 
question  '  how  ? '  and  that  in  most  cases — indeed  in  all — 
we  must  learn  to  be  contented  with  the  answer  to  '  how  ? ' 
The  better  we  can  tell  how  things  are,  the  more  nearly 
shall  we  be  able  to  say  why  they  are. 

Such  a  question  is  applicable  to  all  kinds  of  subjects : 
to  what  our  forerunners  on  this  earth  did ;  how  they 
lived  :  if  we  go  even  further  back,  what  preceded  them  on 
the  earth.  The  history  of  these  inquiries  is  the  function 
of  geology,  palaeontology,  and  palseontological  botany ;  it 
is  continued  through  archseology,  Egyptian  and  Assyrian, 
Greek  and  Roman  ;  it  evolves  into  history,  and  lights  are 
thrown  on  it  by  languages  and  philology;  it  dovetails 
with  literature  and  economics.  In  all  these,  research  is 
possible;  and  a  University  should  be  equipped  for  the 
successful  prosecution  of  inquiries  in  all  such  branches. 

Another  class  of  inquiries  relates  to  what  we  think  and 
how  we  reason ;  and  here  we  have  philosophy  and  logic; 
A  different  branch  of  the  same  inquiry  leads  us  to  mathe- 
matics, which  deals  with  spatial  and  numerical  concepts 
of  the  human  mind,  geometry  and  algebra.  By  an  easy 
transition  we  have  the  natural  sciences  ;  those  less  closely 
connected  with  ourselves  as  persons,  but  intimately  related 
to  our  surroundings.  Zoology  and  botany,  anatomy, 
physiology  and  pathology  deal  with  living  organisms  as 
structural  machines ;  and  they  are  based  on  physics  and 
chemistry,  which  are  themselves  dependent  on  mathe- 
matics. 

Such  inquiries  are  worth  making  for  their  own  sakes. 
They  interest  a  large  part  of  the  human  race ;  and  not  to 
feel  interested  in  them  is  to  lack  intelligence.  The  man 
who  is  content  to  live  from  day  to  day,  glad  if  each  day 
will  but  produce  him  food  to  eat  and  a  roof  to  sleep  under, 
is  but  little  removed  from  an  uncivilised  being.  For  the 
test  of  civilisation  is  prevision ;  care  to  look  forward ;  to 


234    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

provide  for  to-morrow  ;  the  morrow  of  the  race,  as  well  as 
the  morrow  of  the  individual ;  and  he  who  looks  furthest 
ahead  is  best  able  to  cope  with  Nature,  and  to  conquer 
her. 

The  investigation  of  the  unknown  is  to  gather  experience 
from  those  who  have  lived  before  us,  and  to  secure  know- 
ledge for  ourselves  and  for  those  who  will  succeed  us.  I 
see,  however,  that  I  am  insensibly  taking  a  utilitarian 
view;  I  by  no  means  wish  to  exclude  it,  but  the  chief 
purpose  of  research  must  be  the  acquisition  of  knowledge, 
and  the  second  its  utilisation. 

I  will  try  to  explain  why  this  is  so,  and  here  you  must 
forgive  me  if  I  cite  well-known  and  oft- quo  ted  instances. 

If  attempts  were  made  to  discover  only  useful  know- 
ledge (and  by  useful  I  accept  the  vulgar  definition  of 
profitable,  i.e.  knowledge  which  can  be  directly  trans- 
muted into  its  money  equivalent)  these  attempts  would, 
in  many,  if  not  in  most  cases,  fail  of  their  object.  I  do 
not  say  that  once  a  principle  has  been  proved,  and  a 
practical  application  is  to  be  made  of  it,  that  the  working 
out  of  the  details  is  not  necessary.  But  that  is  best  done 
by  the  practical  man,  be  he  the  parson,  the  doctor,  the 
engineer,  the  technical  electrician,  or  the  chemist,  and 
best  of  all  on  a  fairly  large  scale.  If,  however,  the  prac- 
tical end  be  always  kept  in  view,  the  chances  are  that 
there  will  be  no  advance  in  principles.  Indeed,  what  we 
investigators  wish  to  be  able  to  do,  and  what  in  many 
cases  we  can  do,  although  perhaps  very  imperfectly,  is  to 
prophesy,  to  foretell  what  a  given  combination  of  circum- 
stances will  produce.  The  desire  is  founded  on  a  belief 
in  the  uniformity  of  Nature ;  on  the  conviction  that  what 
has  been  will  again  be,  should  the  original  conditions  be 
reproduced.  By  studying  the  consequences  of  varying 
the  conditions  our  knowledge  is  extended;  indeed  it  is 
sometimes  possible  to  go  so  far  as  to  predict  what  will 


THE  FUNCTIONS  OF  A  UNIVERSITY       235 

happen  under  conditions,  all  of  which  have  never  before 
been  seen  to  be  present  together. 

When  Faraday  discovered  the  fact  that  if  a  magnet 
is  made  to  approach  a  coil  of  wire,  an  electric  current  is 
induced  in  that  wire,  he  made  a  discovery  which  at  the 
time  was  of  only  scientific  interest.  That  discovery  has 
resulted  in  electric  light,  electric  traction,  and  the  utilisa- 
tion of  electricity  as  a  motive  power ;  the  development  of 
a  means  of  transmitting  energy,  of  which  we  have  by  no 
means  seen  the  end;  nay,  we  are  even  now  only  at  its 
inception,  so  great  must  the  advance  in  its  utilisation 
ultimately  become. 

When  Hofmann  set  Perkin  as  a  young  student  to 
investigate  the  products  of  oxidation  of  the  base  aniline, 
produced  by  him  from  coal-tar,  it  would  have  been 
impossible  to  have  predicted  that  one  manufactory  alone 
would  possess  nearly  400  large  buildings  and  employ 
5000  workmen,  living  in  its  own  town  of  25,000  inhabi- 
tants, all  of  which  is  devoted  to  the  manufacture  of  colours 
from  aniline  and  other  coal-tar  products.  In  this  work 
alone  at  least  350  chemists  are  employed,  most  of  whom 
have  had  a  university  training. 

Schonbein,  a  Swiss  schoolmaster,  interested  in  chemistry, 
was  struck  by  the  action  of  nitric  acid  on  paper  and 
cotton.  He  would  have  been  astounded  if  he  had  been 
told  that  his  experiments  would  have  resulted  in  the 
employment  of  his  nitrocelluloses  in  colossal  quantity  for 
blasting,  and  for  ordnance  of  all  kinds,  from  the  90- ton 
gun  to  the  fowling-piece. 

But  discoveries  such  as  these,  which  lead  directly  to 
practical  results,  are  yet  far  inferior  in  importance  to 
others  in  which  a  general  principle  is  involved.  Joule 
and  Robert  Mayer,  who  proved  the  equivalence  of  heat 
and  work,  have  had  far  more  influence  on  succeeding  ages 
than  even  the  discoverers  above  mentioned,  for  they  have 


236    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

imbued  a  multitude  of  minds  with  a  correct  understanding 
of  the  nature  of  energy,  and  the  possibility  of  converting 
it  economically  into  that  form  in  which  it  is  most  directly 
useful  for  the  purpose  in  view.  They  have  laid  the  basis 
of  reasoning  for  machines ;  and  it  is  on  machines,  instru- 
ments for  converting  unavailable  into  available  energy, 
that  the  prosperity  of  the  human  race  depends. 

You  will  see  from  these  instances  that  it  is  in  reality 
c  philosophy '  or  a  love  of  wisdom  which,  after  all,  is  most 
to  be  sought  after.  Like  virtue,  it  is  its  own  reward ;  and 
as  we  all  hope  is  the  case  with  virtue  too,  it  brings  other 
rewards  in  its  train;  not,  be  it  remarked,  always  to  the 
philosopher,  but  to  the  race.  Virtue,  pursued  with  the 
direct  object  of  gain,  is  a  poor  thing;  indeed,  it  can 
hardly  be  termed  virtue,  if  it  is  dimmed  by  a  motive. 
So  philosophy,  if  followed  after  for  profit,  loses  its 
meaning. 

But  I  have  omitted  to  mention  another  motive  which 
makes  for  research ;  it  is  a  love  of  pleasure.  I  can 
conceive  no  pleasure  greater  than  that  of  the  poet — the 
maker — who  wreathes  beautiful  thoughts  with  beautiful 
words;  but  next  to  this,  I  would  place  the  pleasure  of 
discovery,  in  whatever  sphere  it  be  made.  It  is  a  pleasure 
not  merely  to  the  discoverer,  but  to  all  who  can  follow  the 
train  of  his  reasoning.  And  after  all,  the  pleasure  of  the 
human  race,  or  of  the  thinking  portion  of  it,  counts  for  a 
good  deal  in  this  life  of  ours. 

To  return: — attempts  at  research,  guided  by  purely 
utilitarian  motives,  generally  fail  in  their  object,  or  at 
least  are  not  likely  to  be  so  productive  as  research  without 
ulterior  motive.  I  am  strengthened  in  this  conclusion  by 
the  verdict  of  an  eminent  German  who  has  himself  put 
the  principle  into  practice ;  who  after  following  out  a 
purely  theoretical  line  of  experiment,  which  at  first 
appeared  remote  from  profit,  has  been  rewarded  by  its 


THE  FUNCTIONS  OF  A  UNIVERSITY       237 

remunerative  utilisation.  He  remarked,  incidentally,  that 
the  professors  in  Polytechnika — (what  we  should  term 
technical  colleges,  intended  to  prepare  young  men  for  the 
professions  of  engineering  and  technical  chemistry) — were 
less  known  for  their  influence  on  industry  than  University 
professors.  The  aim  is  different  in  the  two  cases;  the 
Polytechnika  train  men  for  a  profession ;  the  Philosophical 
Faculty  of  a  German  University  aims  at  imparting  a  love 
of  knowledge ;  and  as  a  matter  of  fact  the  latter  pay  in 
their  influence  on  the  prosperity  of  the  nation  better  than 
the  former.  And  this  brings  me  to  the  fundamental 
premiss  of  my  Oration.  It  is  this : — That  the  best  prepara- 
tion for  success  in  any  calling  is  the  training  of  the  student 
in  methods  of  research.  This  should  be  the  goal  to  be 
clearly  kept  in  view  by  all  teachers  in  the  Philosophical 
Faculties  of  Universities.  They  should  teach  with  this 
object: — to  awaken  in  each  of  their  students  a  love  of  his 
subject,  and  a  consciousness  that  if  he  persevere,  he,  too, 
will  be  able  to  extend  its  bounds. 

Of  course  it  is  necessary  for  the  student  to  learn,  so  far 
as  is  possible,  what  has  already  been  done.  I  would  not 
urge  that  a  young  man  should  not  master,  or  at  all  events 
study,  a  great  deal  of  what  has  already  been  discovered, 
before  he  attempts  to  soar  on  his  own  wings.  But  there 
is  all  the  difference  in  the  world  between  the  point  of 
view  of  the  student  who  reads  in  order  to  qualify  for 
an  examination,  or  to  gain  a  prize  or  a  scholarship, 
and  the  student  who  reads  because  he  knows  that 
thus  he  will  acquire  knowledge  which  may  be  used 
as  a  basis  of  new  knowledge.  It  is  that  spirit  in 
which  our  Universities  in  England  are  so  lamentably 
deficient;  it  is  that  spirit  which  has  contributed  to 
the  success  of  the  Teutonic  nations,  and  which  is 
beginning  to  influence  the  United  States.  For  this  con- 
dition of  things  our  examinational  system  is  largely  to 


238    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

blame ;  originally  started  to  remedy  the  abuses  of  our  Civil 
Service,  it  has  eaten  into  the  vitals  of  our  educational 
system  like  a  canker;  and  it  is  fostered  by  the  farther 
abuse  of  awarding  scholarships  as  the  results  of  examina- 
tions. The  pauperisation  of  the  richer  classes  is  a  crying 
evil;  it  must  some  day  be  cured.  Let  scholarships  be 
awarded  to  those  who  need  them ;  not  to  those  whose 
fathers  can  well  afford  to  pay  for  the  education  of  their 
children.  '  Pot-hunting '  and  Philosophy  have  absolutely 
nothing  in  common. 

There  are  some  who  hold  that  the  time  of  an  investi- 
gator is  wasted  in  teaching  the  elements  of  his  subject.  I 
am  not  one  of  those  who  believe  this  doctrine,  and  for  two 
reasons : — first,  it  is  more  difficult  to  teach  the  elements 
of  a  subject  than  the  more  advanced  branches ;  one  learns 
the  tricks  of  the  trade  by  long  practice ;  and  the  tricks  of 
this  trade  consist  in  the  easy  and  orderly  presentment  of 
ideas.  And  it  is  the  universal  experience  that  senior 
students  gain  more  good  from  instruction  in  advanced 
subjects  by  demonstrators  than  juniors  would  in  elementary 
subjects.  For  the  senior  student  makes  allowances ;  and 
the  keenness  and  interest  of  the  young  instructor  awakens 
his  interest.  Second,  from  the  teachers'  point  of  view,  it 
is  always  well  to  be  obliged  to  go  back  on  fundamentals. 
One  is  too  apt,  without  the  duty  of  delivering  elementary 
lectures,  to  take  these  fundamentals  for  granted ;  whereas, 
if  they  are  recapitulated  every  year,  the  light  of  other 
knowledge  is  brought  to  bear  on  them,  and  they  are  given 
their  true  proportion;  indeed,  ideas  occur  which  often 
suggest  lines  of  research.  It  is  really  the  simplest  things 
which  we  know  least  of;  the  atomic  theory;  the  true 
nature  of  elasticity;  the  cause  of  the  ascent  of  sap  in 
plants;  the  mechanism  of  exchange  in  respiration  and 
digestion;  all  these  lie  at  the  base  of  their  respective 
sciences,  and  all  could  bear  much  elucidation.  I  believe 


THE  FUNCTIONS  OF  A  UNIVERSITY       239 

therefore,  that  it  is  conducive  to  the  furtherance  of  know- 
ledge that  the  investigator  should  be  actively  engaged  in 
teaching.  But  he  should  always  keep  in  view  the  fact 
that  his  pupils  should  themselves  learn  how  to  investi- 
gate ;  and  he  should  endeavour  to  inculcate  that  spirit  in 
them. 

It  follows  that  the  teachers  in  the  Philosophical  Faculty 
should  be  selected  only  from  those  who  are  themselves 
contributing  to  the  advancement  of  knowledge ;  for  if  they 
have  not  the  spirit  of  research  in  them  how  shall  they 
instil  it  into  others  ?  It  is  our  carelessness  in  this  respect 
(I  do  not  speak  of  University  College,  which  has  always 
been  guided  by  these  principles,  but  of  our  country  as  a 
whole)  which  has  made  us  so  backward  as  compared  with 
some  other  nations.  It  is  this  which  has  made  the  vast 
majority  of  our  statesmen  so  careless,  because  so  ignorant, 
of  the  whole  frame  of  mind  of  the  philosopher ;  and  which 
has  made  it  possible  for  men  high  in  the  political  estima- 
tion of  their  countrymen  to  misconceive  the  functions 
of  a  University.  It  is  true  that  one  of  these  functions  of  a 
University  is  to  '  train  men  and  women  fit  for  the  manifold 
requirements  of  the  Empire ' ;  that  we  should  all  heartily 
acknowledge ;  but  no  man  who  has  any  claim  to  university 
culture  can  possibly  be  contented  if  the  University  does 
not  annually  produce  much  work  of  research.  It  is  its 
chief  excuse  for  existence ;  a  University  which  does  not 
increase  knowledge  is  no  University ;  it  may  be  a  technical 
school ;  it  may  be  an  examining  board ;  it  may  be  a 
coaching  establishment ;  but  it  has  no  claim  to  the  name 
University.  The  best  way  of  fitting  young  men  for  the 
manifold  requirements  of  the  Empire  is  to  give  them  the 
power  of  advancing  knowledge. 

It  may  be  said  that  many  persons  are  incapable  of 
exhibiting  originality.  I  doubt  it.  There  are  many 
degrees  of  originality,  as  there  are  many  degrees  of 


240    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

rhyming,  from  the  writer  of  doggerel  to  the  poet,  or  many 
degrees  of  musical  ear,  from  the  man  who  knows  two 
tunes,  the  tune  of  '  God  save  the  King '  and  the  other 
tune,  to  the  accomplished  musician.  But  in  almost  all 
cases,  if  caught  young,  the  human  being  can  be  trained, 
more  or  less ;  and,  as  a  matter  of  fact,  natural  selection 
plays  its  part.  Those  young  men  and  women  who  have 
no  natural  aptitude  for  such  work — and  they  are  usually 
known  by  the  lack  of  interest  which  they  take  in  it— do 
not  come  to  the  University.  My  experience  is  that  the 
majority,  or  at  least  a  fair  percentage  of  those  who  do 
come,  possess  germs  of  the  faculty  of  originating,  germs 
capable  of  development,  in  many  instances,  to  a  very  high 
degree.  It  is  such  persons  who  are  of  most  value  to  the 
country ;  it  is  from  them  that  advance  in  literature  and 
in  science  is  to  be  expected ;  and  many  of  them  will  con- 
tribute to  the  commercial  prosperity  of  the  country.  We 
hear  much  nowadays  of  technical  education ;  huge  sums 
of  money  are  being  annually  expended  on  the  scrappy 
scientific  education  in  evening  classes  of  men  who  have 
passed  a  hard  day  in  manual  labour,  men  who  lack  the 
previous  training  necessary  to  enable  them  to  profit  by 
such  instruction.  It  may  be  that  it  is  desirable  to  pro- 
vide such  intellectual  relaxation ;  I  even  grant  that  such 
means  may  gradually  raise  the  intellectual  level  of  the 
country ;  but  the  investment  of  money  in  promoting  such 
schemes  is  not  the  one  likely  to  bear  the  most  immediate 
and  remunerative  fruit.  The  Universities  should  be  the 
technical  schools ;  for  a  man  who  has  learned  to  investi- 
gate can  bring  his  talents  to  bear  on  any  subject  brought 
under  his  notice,  and  it  is  on  the  advance,  and  not  the 
mere  dissemination  of  knowledge,  that  the  prosperity  of 
a  country  depends.  To  learn  to  investigate  requires  a 
long  and  a  hard  apprenticeship ;  the  power  cannot  be 
acquired  by  an  odd  hour  spent  now  and  again ;  it  is  as 


THE  FUNCTIONS  OF  A  UNIVERSITY       241 

difficult  to  become  a  successful  investigator  as  a  successful 
barrister  or  doctor,  and  it  requires  at  least  as  hard  appli- 
cation and  as  long  a  period  of  study. 

I  do  not  believe  that  it  is  possible  for  young  men  or 
women  to  devote  sufficient  time  during  the  evening  to 
such  work.  Those  who  devote  their  evening  hours  to 
study  and  investigation  do  not  bring  fresh  brains  to  bear 
on  the  subject;  they  are  already  fatigued  by  a  long  day's 
work;  and,  moreover,  it  is  the  custom  in  most  of  the 
colleges  which  have  evening  classes  to  insist  upon  their 
teachers  doing  a  certain  share  of  day  work ;  they,  too,  are 
not  in  a  fit  state  to  direct  the  work  of  their  pupils  nor  to 
make  suggestions  as  to  the  best  method  of  carrying  it  out. 
Moreover,  the  official  evening  class  is  from  seven  to  ten 
o'clock,  and  for  investigation  in  science  a  spell  of  three 
hours  at  a  time  is  barely  sufficient  to  carry  out  success- 
fully the  end  in  view ;  indeed,  an  eight  hours'  day  might 
profitably  be  lengthened  into  a  twelve  hours'  day,  as  it  not 
infrequently  is.  It  is  heartrending  in  the  middle  of  some 
important  experiment  to  be  obliged  to  close  and  postpone 
it  till  a  future  occasion,  when  much  of  the  work  must 
necessarily  be  done  over  again. 

These  are  some  of  the  reasons  why  I  doubt  whether 
University  education,  in  the  Philosophical  Faculty  at 
least,  can  be  successfully  given  by  means  of  evening 
classes. 

Although  my  work  has  lain  almost  entirely  in  the 
domain  of  science,  I  should  be  the  last  man  not  to  do  my 
best  to  encourage  research  in  the  sphere  of  what  is  gener- 
ally called  '  arts.'  In  Germany  of  recent  years  a  kind  of 
institution  has  sprung  up  which  is  termed  a  Seminar. 
The  word  may  be  translated  a  '  literary  laboratory.'  I  will 
endeavour  to  give  a  short  sketch  on  the  way  in  which 
these  literary  laboratories  are  conducted.  After  the 
student  has  attended  a  course  of  lectures  on  the  subjects 

Q 


242    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

to  which  he  intends  to  devote  himself,  and  is  ripe  for 
research,  he  enters  a  Seminar,  in  which  he  is  provided 
with  a  library,  paper,  pens  and  ink,  and  a  subject.  The 
method  of  using  the  library  is  pointed  out  to  him,  and  he 
is  told  to  read  books  which  bear  on  the  particular  subject 
in  question ;  he  is  made  to  collate  the  information  which 
he  gains  by  reading,  and  to  elaborate  the  subject  which 
is  given  him.  Naturally  his  first  efforts  must  be  crude,  but 
ce  n'est  que  le  premier  pas  qui  cotite.  It  probably  costs  him 
blame  at  the  hands  of  his  instructor ;  after  a  few  unsuc- 
cessful efforts,  however,  if  he  has  any  talent  for  the  par- 
ticular investigation  to  which  he  has  devoted  himself, 
his  efforts  improve  and  at  last  he  produces  something 
respectable  enough  to  merit  publication.  Thus  he  is 
exposed  to  the  criticism  of  those  best  competent  to  judge, 
and  he  is  launched  in  what  may  be  a  career  in  Historical, 
Literary,  or  Economic  research. 

Such  a  Seminar  is  carried  on  in  philological  and 
linguistic  studies,  in  problems  of  economy  involving 
statistics,  in  problems  of  law  involving  judicial  decision, 
and  of  history  in  which  the  relations  between  the  develop- 
ment of  the  various  phases  in  the  progress  of  nations  is 
traced.  The  system  is  borrowed  from  the  well-known 
plan  of  instruction  in  a  physical  or  chemical  laboratory. 
Experiments  are  made  in  literary  style.  These  experi- 
ments are  subjected  to  the  criticism  of  the  teacher,  and 
thus  the  investigator  is  trained.  But  it  may  be  objected 
that  the  youths  who  frequent  our  Universities  have  not  a 
sufficient  knowledge  of  facts  connected  with  such  subjects 
to  be  ^capable  of  at  once  entering  on  a  training  of  this 
kind.  That  may  be  so ;  if  it  is  the  case,  our  schools  must 
look  to  it  that  they  provide  sufficient  training.  Even 
under  present  circumstances,  however,  I  do  not  think  I 
am  mistaken  in  supposing  that  a  young  man  or  woman 
who  enters  a  University  at  the  age  of  eighteen  years  with 


THE  FUNCTIONS  OF  A  UNIYEESITY       243 

the  intention  of  spending  three  years  in  literary  or  his- 
torical studies  will  not  at  the  end  of  the  second  year  be 
more  benefited  by  a  course  at  the  Seminar,  even  though  it 
should  result  in  no  permanent  addition  to  literature  or 
history,  than  if  he  were  to  spend  his  time  in  mere  assimi- 
lation. It  is  not  the  act  of  gaining  knowledge  which 
profits,  it  is  the  power  of  using  it,  and  while  in  order  to 
use  knowledge  it  is  necessary  to  gain  it,  yet  a  training  in 
the  method  of  using  knowledge  is  much  more  important 
and  profitable  than  a  training  in  the  method  of  gaining 
it.  I  do  not  know  whether  there  exists  in  this  country  a 
single  example  of  the  continental  Seminar ;  there  was  some 
talk  of  founding  such  a  literary  laboratory  in  University 
College,  but,  as  usual,  the  attempt  was  frustrated  by  a 
lack  of  funds ;  the  attempt  would  also  have  been  frustrated 
by  the  requirements  of  the  present  system  of  examination 
in  the  University  of  London ;  but  there  is,  fortunately, 
good  hope  of  changing  that  system  and  of  developing  the 
minds  of  students  on  those  lines  which  have  proved  so 
fruitful  where  they  have  been  systematically  followed.1 

There  is  one  subject,  of  which  the  votaries  are  so  few, 
that  it  is  difficult  to  treat  in  the  same  manner  as  those 
literary  and  scientific  subjects  of  which  I  have  been  speak- 
ing; that  subject  is  mathematics.  While  many  persons 
have  a  certain  amount  of  mathematical  ability  which 
they  cultivate  as  a  means  to  an  end,  those  who  are  born 
mathematicians  are  as  few  as  those  who  are  born 
musicians.  I  have  had  the  privilege  of  discussing  this 
question  with  one  of  the  foremost  mathematicians  of 
Europe — Professor  Klein  of  Gottingen.  He  tells  me  that 
while  he  is  content  for  the  most  part  to  treat  mathematics 
as  a  technical  study,  imparting  to  his  pupils  so  much  as  is 
necessary  for  them  to  use  it  easily  as  an  instrument,  he 

1  Several  Seminars  have  now  been  started  at  University  College 
(Sept.  1908). 


244    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

discourages  young  men,  unless  they  are  especially 
endowed  by  Nature,  from  pursuing  the  study  of  mathe- 
matics with  the  object  of  cultivating  a  gift  for  that 
subject.  Especially  gifted  men  occasionally  turn  up,  and 
those  who  possess  mathematical  insight  are  able  to  profit 
by  the  instruction  of  the  professor  in  developing  some 
special  branch  of  the  subject.  Mathematical  problems, 
he  tells  me,  are  numerous,  but  they  demand  such  an  ex- 
tensive knowledge  of  what  has  already  been  done  that 
very  few  persons  who  do  not  devote  their  lives  to  the  sub- 
ject are  able  to  cope  with  them,  and  it  is  only  those  who 
are  born  with  a  mathematical  gift  who  can  afford  to 
devote  their  lives  to  mathematics,  for  the  standard  is  high, 
and  the  prizes  are  few. 

Many,  I  suppose,  who  are  at  present  listening  to  me 
would  be  disappointed  were  I  not  to  refer  to  the  functions 
of  a  University  with  reference  to  examinations.  A  long 
course  of  training,  lasting  now  for  the  best  part  of  seventy 
years,  has  convinced  the  population  of  London  that  the 
chief  function  of  a  University  is  to  examine.  Believe  me, 
the  examination  should  play  only  a  secondary  part  in  the 
work  of  a  University.  It  is  necessary  to  test  the  acquire- 
ments of  the  students  whom  the  teachers  have  under 
their  charge,  but  the  examination  should  play  an  entirely 
subordinate  part.  To  be  successful  in  examinations  is 
unfortunately  too  often  the  goal  which  the  young  student 
aims  at,  but  it  is  one  which  all  philosophical  teachers 
deprecate.  To  infuse  into  his  pupils  a  love  of  the  sub- 
ject which  both  are  at  the  same  time  teaching  and  learn- 
ing, is  the  chief  object  of  an  enthusiastic  teacher;  there 
should  be  an  atmosphere  of  the  subject  surrounding  them 
— an  umbra — perhaps  I  should  call  it  an  aura;  for  it 
should  exert  no  depressing  influence  upon  them.  The 
object  of  both  classes  of  students  (for  I  count  the  teacher 
a  student)  should  be  to  do  their  best  to  increase  know- 


THE  FUNCTIONS  OF  A  UNIVERSITY       245 

ledge  of  the  subject  on  which  they  are  engaged.  That 
this  is  possible,  many  teachers  can  testify  to  by  experi- 
ence; and  it  is  the  chief  lesson  learned  by  a  sojourn  in  a 
German  laboratory.  Where  each  student  is  himself 
engaged  in  research,  interest  is  taken  by  the  students  in 
each  others'  work;  numerous  discussions  are  raised 
regarding  each  questionable  point;  and  the  combined 
intelligence  of  the  whole  laboratory  is  focussed  on  the 
elucidation  of  some  difficult  problem.  There  is  nothing 
more  painful  to  witness  than  a  dull  and  decorous  labora- 
tory, where  each  student  keeps  to  his  own  bench,  does  not 
communicate  with  his  fellow-students,  does  not  take  an 
interest  in  their  work,  and  expects  them  to  manifest  no 
interest  in  his.  It  is  only  by  friction  that  heat  can  be 
produced,  and  heat,  by  increasing  the  frequency  of 
vibration,  results,  as  we  know,  in  light. 

The  student  should  look  forward  to  his  examination 
not  as  a  solemn  ordeal  which  he  is  compelled  to  go 
through  with  the  prospect  of  a  degree  should  he  be  suc- 
cessful, but  as  a  means  of  showing  his  teacher  and  his 
fellows  how  much  he  has  profited  by  the  work  which  he 
has  done ;  those  who  pursue  knowledge  in  this  spirit  and 
those,  be  it  remarked,  who  examine  in  this  spirit  will  look 
forward  to  examination  with  no  apprehension ;  not,  per- 
haps, with  joy,  for  after  all  it  is  a  bore  to  be  examined 
and  perhaps  a  still  greater  bore  to  examine,  but  it  is  a 
necessary  step  for  the  student  in  gaining  self-assurance 
and  the  conviction  of  having  profited  by  his  exertions ; 
and  for  the  teacher,  as  a  means  of  insuring  that  his 
instruction  has  not  been  profitless  to  his  student.  In  this 
connection  I  cannot  refrain  from  remarking,  that  that 
genius  for  competition  which  has  over-ridden  our  nation 
of  England,  appears  to  me  to  be  misplaced.  Far  too 
much  is  thought  of  the  top  man ;  very  likely  the  second 
or  even  the  tenth,  or  it  may  be  the  fiftieth  has  a  firmer 


246    ESSAYS  BIOGRAPHICAL  AND  CHEMICAL 

grasp  of  his  subject,  and  in  the  long-run  would  display 
more  talent.  Let  us  take  comfort,  however,  in  the 
thought,  that  the  day  of  examinations,  for  the  sake  of 
examinations,  is  approaching  an  end. 

It  may  surprise  many  to  learn  that  the  suggestion  that 
in  England  teachers  do  not  usually  examine  their  own 
pupils  for  degrees,  is,  abroad,  received  in  a  spirit  of  sur- 
prise not  unmixed  with  incredulity.  Americans  and 
Germans  to  whom  I  have  mentioned  this  state  of  matters, 
cannot  realise  that  the  teacher  is  not  considered  fit  to  be 
trusted  to  examine  his  own  pupils,  and,  singular  to  state, 
they  maintain  that  no  one  else  can  possibly  do  so  with 
any  attempt  at  fairness ;  it  appears  to  them,  as  it  appears 
to  me,  an  altogether  untenable  position  to  hold  that  a 
man  selected  to  fill  an  important  professorship,  after  many 
years'  trial  in  a  junior  position,  should  be  suspected  of 
such  (shall  I  say)  ambiguous  ideas  regarding  common 
honesty,  that  he  will  always  arbitrate  unfairly  in  favour  of 
his  own  pupils.  Such  a  supposition  is  an  insult  to  the 
professor ;  and  the  exclusion  of  the  teacher  elevates 
examination  to  the  position  of  a  fetish ;  it  is  that,  together 
with  the  spirit  of  emulation  and  competition,  which  has 
done  so  much  to  ruin  our  English  education.  The  idea  of 
competitive  examination  is  so  ingrained  in  the  minds  of 
Englishmen,  that  it  is  difficult  for  them  to  realise  that 
the  object  of  a  University  is  not  primarily  to  examine  its 
pupils,  but  to  teach  them  to  teach  themselves  ;  and  also 
they  have  still  to  acquire  the  conviction  that  students 
should  be  found  not  merely  among  the  alumni  of  the 
University  but  also  among  all  members  of  the  staff.  The 
spirit  which  should  prevail  with  us  should  be  the  spirit 
of  gaining  knowledge — gaining  knowledge  not  for  the 
satisfaction  of  one's  own  sense  of  acquisitiveness,  but  in 
order  to  be  able  to  increase  the  sum- total  of  what  is 
known.  All  should  work  together,  senior  and  junior  staff, 


THE  FUNCTIONS  OF  A  UNIVERSITY       247 

graduates  and  undergraduates,  in  order  to  diminish  man's 
ignorance. 

To  sum  up.  As  it  exists  at  present,  a  University  is  a 
technical  school  for  theology,  law,  medicine,  and  engineer- 
ing. It  ought  to  be  also  a  place  for  the  advancement  of 
knowledge,  for  the  training  of  philosophers,  of  those  who 
love  wisdom  for  its  own  sake ;  and  while  as  a  technical 
school  it  exercises  a  useful  function  in  preparing  many 
men  and  women  for  their  calling  in  life,  its  philosophical 
faculty  should  impart  to  those  who  enter  its  halls  that 
faculty  of  increasing  knowledge  which  cannot  fail  to  be 
profitable  not  only  to  the  intellect  of  the  nation,  but  also 
to  its  industrial  prosperity.  I  regard  this  as  the  chief 
function  of  a  University. 


Yx5 

OF  THE 

UNIVERSITY 

OF 

£*Urr- 


Printed  by  T.  and  A.  CONSTABLE,  Printers  to  His  Majesty 
at  the  Edinburgh  University  Press 


A 


THE  LAST  DATE      f 


MAV    5 


APR  15 


4  1940 


OCT 
OCT 


1943 


.-!,'« 


LD  2lA-45m-9,'67 
(H5067slO)476B 


General  Library 

University  of  California 

Berkelev 


YB   I74£ 


u.c.  BERKELEY  LIBRARIE; 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


